Known issues up to firmware 2022.9

Known for all firmware releases up to 2021.9 on all supported PLCnext Control devices:

Changes made as the Linux® root user (such as manual changes in configuration files) can cause problems when updating the firmware to release 2022.0 LTS. In this case the controller has to be reset to default settings (type 1) before updating the firmware successfully. The reason for this issues is that changes made by the Linux root user are stored in the upperdir folder of the Overlay File System (overlayFS). If a new firmware release brings along changes in the same files, those firmware changes cannot become active due to the previous changes in the upperdir folder. Even Linux® commands like adduser or addgroup cause changes of their corresponding configuration files in the overlayFS.

Known for firmware 2020.3 and 2020.6 on all supported PLCnext Control devices - fixed with firmware 2021.0 LTS:

If the controller is rebooted using the Linux command sudo reboot or by means of the RSC service IDeviceControlService::RestartDevice(), a system watchdog may occur in rare cases. Because the RSC service is also used by the Reboot button in the PLCnext Engineer cockpit, it can also occur after using that button. As a consequence only a Cold Start is possible when the controller is subsequently booted, so all retain variables are reinitialized. This behavior does not occur when the operating voltage is switched off and the controller is then booted.

Known from firmware 2020.3 to 2021.6 on all supported PLCnext Control devices:

The system watchdog is not yet active during the startup phase if you start C++ extensions very early. If the user code causes a crash during this phase, this can lead to an endless boot loop. You can solve the problem by removing the SD card before rebooting.

Known from firmware 2020.6 on all supported PLCnext Control devices:

Setting local time zones is not fully supported. After setting a local time zone, unexpected results may occur when reading out times from different contexts (RTC-S FB, OPC UA®, SPNS LOG).

Known for firmware 2021.0 LTS on all supported PLCnext Control devices:

Coming from 1.x or 2019.x firmware, the 2021.0 LTS firmware update removes the following files that are not edited by PLCnext Engineer nor are they intended to be modified by the user:

• /opt/plcnext/projects/Default/Plc/Eclr/Default.eclr.config 
• /opt/plcnext/projects/Default/Plc/Gds/Default.gds.config 
• /opt/plcnext/projects/Default/Plc/Meta/Default.meta.config 
• /opt/plcnext/projects/Default/Plc/Plm/Plm.config 
• /opt/plcnext/projects/Default/Plc/Esm/Default.esm.config 
• /opt/plcnext/projects/Default/Plc/Esm/ServiceTask.esm.config 
• /opt/plcnext/projects/Default/Plc/Esm/Globals.esm.config 

Known from firmware 2021.6 to 2024.6 on all supported PLCnext Control devices - fixed with firmware 2025.0:

If a user component causes a crash before the system watchdog is activated the firmware terminates and the controller is available via SSH only. (Note: The system watchdog is activated just before the IControllerComponent::Start() method is invoked.)

Known from firmware 2021.6 on AXC F 3152:

Reset to default setting type 2 can only be performed with a running Linux system. If a user makes changes in the Overlay File System (overlayFS) that lead to problems booting the system, then resetting the device via the reset button is not possible.  
Only known workaround: Boot the controller with an external SD card, copy the overlayFS to this external SD card and delete the overlayFS on the controller after that.

Known from firmware 2022.0 LTS to 2024.6 on AXC F 1152 and AXC F 2152 - fixed with firmware 2025.0:

An attempt to set the system time of the controller to a timepoint in year 2038 or later results in a system watchdog. 

Known for firmware 2022.6 on all supported PLCnext Control devices - fixed with hotfix 2022.6.2 for RFC 4072S, firmware 2022.9 for AXC F 2152, firmware 2023.0 LTS for AXC F 1152 and AXC F 3152:

If a firmware version < 2021.0 LTS  on a controller is updated to a higher version, the WBM of the controller is no longer accessible. The WBM is only accessible again after the controller has been restarted one more time.

Known for firmware 2020.0 LTS to 2021.0 LTS on all supported PLCnext Control devices - fixed with firmware 2021.6:

The DBG LED or touch panel indicator should signal if a variable has been set via forcing in debug mode in the PLC project. This behavior is currently not supported: Despite forcing the variable the DBG LED or touch panel indicator remains off.

Known for firmware 2020.3 on RFC 4072S - fixed with firmware 2020.6:

The removal of the fan during operation is not detected correctly due to a technical feature.

Known for ALL firmware versions on AXC F 3152 with left-side extension

If the AXC F 3152 is used along with any left-side extension module (e.g. AXC F XT SPLC 1000, AXC F XT SPLC 3000, AXC F XT IB, AXC F XT ETH 1TX, AXC F XT PB, AXC F XT ML 1000, ...), it is not ensured, that the retentive data is stored during a short-term power failure (voltage drop). If the retentive data cannot be stored (e.g. due to an ESM task watchdog), a cold restart is required which resets all retentive variables to their initial values. In order to prevent this data loss, please use a power supply with integrated UPS, e.g. Phoenix Contact QUINT4-UPS/24DC/24DC/10 (item number 2907066).

Known for firmware 2020.6 on AXC F 3152 and RFC 4072S:

If the SD card is removed during operation and then the supply voltage is disconnected, the device will operate with the internal voltage buffer until it is discharged. This can take up to 30 seconds.

Known for firmware 2021.0 LTS or newer on AXC F 1152 and AXC F 2152:

The Link and the Active LEDs on the X1 and X2 network interfaces are not illuminated when a 10BaseT connection is used.

Known for firmware 2021.6 on AXC F 1152 and AXC F 2152:

In rare cases, the controller may no longer recognize the SD card after an interruption of the power supply. All LEDs flash and the controller cannot be connected via Ethernet. Only some 2 GB SD cards are affected by this. 

Known for firmware 2020.6 and newer on all supported PLCnext Control devices:

DHCP can only be activated for Ethernet adapters that are not assigned as PROFINET controllers or PROFINET devices. To make the settings effective in the network, the device must be restarted.

Known for firmware 2020.6 on all supported PLCnext Control devices,
and persisting from firmware 2021.0 LTS and newer in the touch panel of RFC 4072S:

In general, when DHCP is switched on, the current IP settings are not yet displayed in the WBM or on the touch display, but the static settings last set are displayed.

Known for firmware 2020.6 and 2021.0 LTS on RFC 4072S, and on AXC F 2152 and AXC F 3152 if used in combination with an AXC F XT ETH 1TX extension module:

If there are several Default Gateway settings, only the setting of LAN1 is used for all LAN adapters. Different settings of other LAN adapters (i.e. for LAN2) are ignored.

Known for firmware 2020.6 and 2021.0 LTS on AXC F 2152 with AXC F XT ETH 1TX attached:

If both network adapters in the PLCnext Control and the extension are configured with the same subnet, then the PROFINET Controller functionality will not work as desired. A proper connection setup is not possible with this configuration.

Known for firmware 2020.0 LTS and 2020.3 on all supported PLCnext Control devices:

The PROFINET connection setup can take a long time in combination with a very large PROFINET structure.

Known from firmware 2020.0 LTS to 2020.6 on all supported PLCnext Control devices:

Frequent calls of PROFINET Read Record and Write Record function blocks may disturb the communication to the corresponding AR. A connection termination may occur.

Known for firmware 2020.3 on AXC F 1152 and AXC F 2152:

After switching off MRP, a restart of the PLCnext Control is required in order for it to work properly.

Known for firmware 2020.3 and 2020.6 on all supported PLCnext Control devices:

If firmware 2020.3.1 or 2020.6 is downgraded to an older version, the PROFINET name is lost.

Known from firmware 2021.0 LTS on AXC F 1152 and AXC F 2152:

The use of a PROFINET cycle time of 1 ms leads to a deviation of the jitter behavior required by the controller certification. Operation in  this state is possible but not recommended.

Known from firmware 2021.0 LTS to 2022.3 on all supported PLCnext Control devices - fixed with firmware 2022.6:

A PROFINET device connection may be terminated and re-established if cyclic tasks at all ESM cores are used, and if these tasks have an execution duration longer than the configured monitor time of a PROFINET device. 

• Check the execution duration in your code, set by usingESM_DATA.ESM_INFOS[..].TASK_INFOS[..].MAX_EXEC_DURATION.
• Compare to the monitor time set with PLCnext Engineer in the PLANT area → Interface node → Settings tab → Monitor time.

Known from firmware 2021.6 on AXC F 2152, AXC F 3152, and RFC 4072S:

PROFINET PRL (Phoenix Redundancy Layer) is not supported. Firmware release 2021.0 LTS was the last release supporting PRL, newer releases do not support this feature.

Known for firmware 2022.6 and 2022.9 on all supported PLCnext Control devices:

If a PROFINET Device indicates a module difference (ModuleDiffBlock) without corresponding submodule differences, this module difference is not reported in the related notification. This behavior has been observed with PROFINET Devices from other vendors than Phoenix Contact.

Additionally this module difference is not shown in the Diagnostics - PROFINET WBM page nor can it be retrieved via RSC IArConfigurationService, or via the IEC 61131-3 function block GET_MODULE_DIFF_BLOCK.

Known for firmware 2021.9 on AXC F 2152 and AXC F 3152 with AXC F XT PB attached - fixed with firmware 2022.0 LTS:

If a PROFIBUS station is missing after successful first commissioning, this is not indicated via the system variables or the diagnostic interface. Only the status LED on the AXC F XT PB extension module indicates this problem.

Known for firmware 2021.9 on AXC F 2152 and AXC F 3152 with AXC F XT PB attached - fixed with firmware 2022.0 LTS:

The EXT LED on the controller incorrectly lights up red instead of green if the PROFIBUS left alignment is connected correctly. However, this does not affect the function of the left alignment.

Known from firmware 2021.9 on AXC F 2152 and AXC F 3152 with AXC F XT PB attached:

If a faulty PROFIBUS configuration is set after successful first commissioning, this is not displayed via the system variables or the diagnostic interface. The affected PROFIBUS station is not commissioned, but is displayed as ready.

Known from firmware 2021.9 to 2022.3 on AXC F 2152 and AXC F 3152 with AXC F XT PB attached:

The acyclic PROFIBUS communication DPV1 is not yet supported.

Known for firmware 2020.3 and 2020.6 on all supported AXC F x152 stations containing an Axioline Smart Elements backplane:

If an Axioline bus contains a power terminal and a Smart Elements module with empty slots, the bus will not restart after a power failure.

Known from firmware 2021.6 to 2023.9 on AXC F 1152, AXC F 2152 and AXC F 3152 devices:

Some Axioline modules (e.g. analog outputs) provide status information in their process data. In case of a module error (e.g. loss of power supply) these process data inputs are filled with an error code. However, in certain situations these process data inputs return 0 instead of the error code. 
Only process data inputs of modules connected to the controller's local bus are affected. Not affected are retrieving module errors via PDI request as well as displaying these errors at the WBM page Diagnostics - Local Bus.

Known for all firmware releases on AXC F 1152, AXC F 2152, and AXC F 3152 devices:

If the firewall is activated via WBM, the operation of EtherNet/IP™ is no longer possible. This can be remedied by subsequently activating the ports:

• Incoming connections: port 44818
• Outgoing connections: port 2222

Known for firmware 2020.0 LTS on RFC 4072S:

After downloading a safety-related project, a new connection to PLCnext Engineer is sporadically not possible. The following error message is displayed: "Error during login! A communication error was detected".

Known for firmware 2020.0 LTS on all supported PLCnext Control devices, and for firmware 2020.3 on AXC F 3152:

If you initiate a warm start in PLCnext Engineer and this is not possible internally, a cold start is performed automatically, i.e., the retain variables are reinitialized.

Known from firmware 2020.0 LTS on all supported PLCnext Control devices:

During a PLCnext Engineer program download (both total and "changes only"), the web server returns a 503 error ("busy") for requests to the HMI pages.

Known for firmware 2020.0 LTS and 2020.3 on AXC F 1152, AXC F 2152, and RFC 4072S:

After debugging a PLCnext Engineer project with breakpoints the project may stop immediately after restarting.

Known for firmware 2020.3 and 2020.6 on all supported PLCnext Control devices:

When debugging IEC 61131 code with activated breakpoints, display errors may occur in the call sequence function and variable contents.

Known for firmware 2020.3 to 2023.3 on all supported PLCnext Control devices - fixed with firmware 2023.6:

Sporadically a PLCnext Engineer project may reject the Download changes command without giving a reason.

Known for all firmware versions on all supported PLCnext Control devices:

Using PLCnext Engineer, setting and activating a breakpoint in a code which is located in one of the ESM event tasks "Cold start", "Warm start", "Hot start" or "Stop" can cause an error: If this event task is executed, then the communication with PLCnext Engineer is interrupted and the PLC switches to an error state. The PLC needs to be rebooted.

Known for firmware 2021.6 and 2021.9 on all supported PLCnext Control devices - fixed with firmware 2022.0 LTS:

Sporadic communication errors may occur between PLCnext Engineer and the controller.
Remedy: Reboot the controller.

Known for firmware 2022.0 LTS (initial release) on AXC F 1152 and AXC F 2152 - fixed with firmware 2022.0.4 LTS:

Depending on the history of firmware releases installed on a particular PLC it can happen that after updating to firmware 2022.0 LTS a web browser can no longer connect to the PLCnext Engineer HMI at the PLC. As remedy the PLC needs to be reset to default settings (type 1).

Known for firmware 2022.0 LTS on RFC 4072S - fixed with firmware 2022.6:

Used and free data memory for an IEC 61131-3 application is not displayed correctly in PLCnext Engineer.

Known for firmware 2020.6 and 2021.0 LTS on all supported PLCnext Control devices:

When a Solution App is uninstalled by the PLCnext Store, it can happen that the controller then no longer reacts to any actions by the PLCnext Store, although it reports the statusonline. A system watchdog was also sporadically observed. This behavior has not been observed when using the offline deactivation in the WBM for uninstalling a solution app.

Known from firmware 2020.6 to 2022.9 on all supported PLCnext Control devices:

Sporadically it can happen that a restart of the firmware requested by an app installation does not work properly. If the firmware does not start up correctly, the controller can be restarted by one of the following possible actions:

• Restart of the firmware via SSH (/etc/init.d/plcnext restart)
• Reboot of the controller via SSH
• Power reset of the controller

Known from firmware 2021.9 on all supported PLCnext Control devices:

Licence operations, such as adding or removing a licence, include cryptographic operations and hence shall only be performed if the PLC is stopped. This may avoid side effects due to preempting the license operations by tasks running with higher priority.

Known for firmware 2020.6 on AXC F 2152:

After resetting the controller there is no TrustStore with the name „proficloudv3“. The TrustStore is necessary for the update via Proficloud.

Workaround: Re-create the TrustStore in the WBM on the controller.

Known from firmware 2022.9 to 2023.3 on all supported PLCnext Control devices - fixed with hotfix 2023.0.7 and firmware 2023.6:

When Proficloud is configured to cache values (WBM setting Remanent Buffering Enabled) and when the connection between PLC and Proficloud is broken, the consumed memory increases. If this situation continues for a too long period, it may even lead to a system watchdog.

Known up to firmware 2020.0 LTS on all supported PLCnext Control devices:

C++ projects that were created using WorkerThread in SDK release 2019.0 LTS have to be compiled again using an SDK version ≥ 2019.3. Otherwise, the WorkerThread is not loaded after restart of the application.

Known from firmware 2020.0 LTS to 2022.0 LTS (initial release) on AXC F 1152, AXC F 2152, and AXC F 3152 - fixed with hotfix 2022.0.5 LTS for AXC F 3152; firmware AXC F 2152 for AXC F 2152, firmware 2022.6 for AXC F 1152:

An ESM event task could be executed only up to 2,147,483,648 times (1,024³x2) after power on. This affected mainly the Interbus cycle end ESM event task. This task is available for the AXC F controllers in combination with AXC F IL ADAPT or  AXC F XT IB extension modules.

Known for firmware 2020.3 on all supported PLCnext Control devices:

With the GNU compiler types GCC (8.3.0, 9.2.1) used, a quadratic increase in compilation time and memory consumption on the desktop PC is observed when very large structures are used. Note this behavior if you use a large number of ports in PLCnext Technology applications (e.g. connection of a very large number of Simulink® signals).

Known for firmware 2020.6 on all supported AXC F x152 devices:

A task watchdog may sporadically occur with a low-priority PLC task with a cycle time in the range of seconds if the running PLC project is being stopped and immediately restarted with a cold/warm/hot start.

Known from firmware 2020.6 on all supported PLCnext Control devices:

If Event, EventTask, ServiceTask or Globals is used as the name of a task in a user program then an error condition of the controller occurs when downloading the project to the controller. This is because these class names are already used internally.

Known for firmware 2021.6 on all supported AXC F x152 devices:

If a fieldbus I/O of data type Bitstring or OctetString is connected to a program port of data type ARRAY, only the value of the first ARRAY element is transferred. The remaining elements are not copied.

Known for firmware 2021.6 and 2021.9 on all supported PLCnext Control devices:

If the socket of the classes Arp::System::Commons::Ipc::IpcSocket, Arp::System::Commons::Net::Socket, and Arp::System::Commons::Net::TlsSocket is shut down, the Select() method returns true. Compared to BSD sockets, this behavior is unexpected. As this is a legacy method it is now remarked as deprecated. With firmware version 2022.0 LTS and newer the Poll() method is implemented.

Known from firmware 2021.6 to 2024.6 on all supported PLCnext Control devices - fixed with firmware 2025.0:

With the SDK version 2021.6 the language standard C++ 17 has been set in the compiler options (-std=c++17). The firmware itself is also compiled with this option set. Besides some general C++ issues related to this C++17 standard, the following issue is related to PLCnext Technology:
C++ 17 introduces the data type std::byte which is unfortunately not compatible with Arp::byte. Therefore, if the namespaces std and Arp are both active the compilation, this results in an error. In this case existing C++ sources have to be adjusted so that they explicitly use Arp::byte (e.g. by adding using byte = Arp::byte;). 
From firmware version 2025.0 the data type Arp::byte is mapped to std::byte". 

Known from PLCnext Technology Toolchain 2020.0 LTS to 2021.0 LTS:

The PLCnext CLI must be used with an SDK for the same release. Downward compatibility throughout releases cannot be guaranteed. From the 2021.6 release, the PLCnext CLI comes as a separate file. See the Tool downloads overview for compatible releases, and PLCnext CLI for procedures with newer firmware releases.

OpenSSL 3 on Linux®

Known for the PLCnext Technology Toolchain from version 2022.0 LTS up to version 2024.0 LTS:

The PLCnext CLI does not work with OpenSSL 3 on Linux. The .Net™ version 6 that is used in the toolchain requires OpenSSL 1.1. This was rectified by a Microsoft update of their .Net™ version. As a workaround with under PLCnext Technology Toolchain ≤2024.0 LTS and e.g. Ubuntu 22.04 LTS, you need to install the OpenSSL 1.1 manually:
wget http://security.ubuntu.com/ubuntu/pool/main/o/openssl/libssl1.1_1.1.1f-1ubuntu2.23_amd64.deb
sudo apt-get install ./libssl1.1_1.1.1f-1ubuntu2.23_amd64.deb

Known for firmware 2020.0 LTS to 2020.6 on all supported PLCnext Control devices:

With extended retain handling in the context of this firmware, the retain variables are reinitialized by a cold start when downgrading to firmware 2020.3 or older. A previous saving of the retain variables by the user is not supported with firmware version 2020.6 or older.

Known for all firmware releases on all supported PLCnext Control devices:

After a system watchdog, only a cold start can be performed when the controller is started. The retain variables are set to their respective initialization values.

Known for firmware 2020.0 LTS or newer on all supported PLCnext Control devices:

If a firmware 2020.0 LTS or newer is downgraded to 2019.9 or older and then upgraded again to firmware version 2020.0 LTS or newer, a Cold Restart is performed. The retain variables are set to their default values.

Known for firmware 2020.3 or newer on all supported PLCnext Control devices:

If a requested warm start is not possible to execute via PLCnext Engineer, an implicit Cold Restart is automatically executed. The retain variables are set to their initialization value. From firmware 2021.0 LTS, a dedicated state of the retain values can be restored from a backup.

Known for firmware 2020.0 LTS on RFC 4072S:

If a task with priority 0 is created on ESM2, a prolonged cycle of the safety project may occur. For this reason, select a priority >0 for a task on ESM2.

Known up to 2024.6 on AXC F 1152 and AXC F 2152 in combination with AXC F XT SPLC 1000 or AXC F XT SPLC 3000, and on RFC 4072S – fixed with 2025.0:

If the Download Changes mechanism (Write and Start Project Changes in PLCnext Engineer) is used along with the SPLC 1000/3000, please take into account a possible malfunction in case the following steps have been performed: 

1. A safety-related project is downloaded to the safety-related controller. 
2. A non-safety-related project is downloaded to the standard controller. 
3. A modified safety-related project is downloaded to the safety-related controller. 
4. An attempt is made to change the non-safety-related project using "Download Changes" (Write and Start Project Changes in PLCnext Engineer), which is rejected by the PLCnext firmware of the standard controller (for example, by changing the task configuration).  
5. The device is restarted. (for example, voltage failure and recovery, request for restart in PLCnext Engineer) 

Attention: After the restart, the safety-related controller executes the original safety-related project from step 1. In order to prevent the described behavior, please additionally carry out the following measures after every change of the safety project:  

• Perform a restart in the PLCnext Engineer software in the Cockpit editor of the standard controller or switch off the supply voltage of the device for at least 30 s and then switch it on again (power reset). 
• Compare the CRC checksum of the safety-related project using the system variables of the safety-related controller or in the Cockpit Safe PLC in the PLCnext Engineer software with the original CRC checksum before the restart.

Known for firmware 2020.0 LTS on all supported PLCnext Control devices, and for firmware 2020.3 on AXC F 3152:

If the use of preexisting C++ applications (Function Extensions) results in mixed operation of the OpenSSL versions 1.0.2 and 1.1.1, the controller does not boot.

Recommended: If you are using an app of the type "Function Extension" from the PLCnext Store, check whether an update is available in the PLCnext Store.

Known for firmware 2020.3 on AXC F 1152, AXC F 2152, and RFC 4072S:

For security reasons, applications should no longer be linked against the outdated OpenSSL version 1.0.2.

Known for firmware 2020.3 on AXC F 1152, AXC F 2152, and RFC 4072S:

Updating the OpenSSL version 1.0.2 to version 1.1.1 can lead to problems with existing C++ applications that are based on this and run in the same process (e.g. function extensions). In the event of incompatibility, the firmware may not start up.

Recommended: If you are using an app of the type "Function Extension" from the PLCnext Store, check whether an update is available in the PLCnext Store.

Known for firmware 2020.3 or newer on all supported PLCnext Control devices:

Access to long STRING variables outside the application is limited to 511 bytes. This concerns reading and writing via the RSC services IDataAccessService and ISubscriptionService. These services are used by OPC UA®, PLCnext Engineer HMI and the online functions of PLCnext Engineer, among others.

The same applies for WString variables (available from firmware 2021.6). Please note that WString variables are converted to UTF8 when accessed via RSC services.

Known for firmware 2020.6 on all supported PLCnext Control devices:

In the IDeviceStatusService RSC service, the Status.Memory.Usage.Percent parameter no longer returns a value with the following user roles:

• Engineer
• Commissioner
• Service
• DataViewer
• DataChanger
• Viewer
• UserManager

Known up to firmware 2024.0 LTS on all PLCnext devices - fixed with hotfix 2024.0.3 LTS:

If the REST ReadVariables command is used with POST then the JSON object created from the content is not deleted properly and causes a system watchdog due to the memory leak. This issue will be fixed a.s.a.p.; meanwhile, use the GET flavor of that ReadVariables command.

Known from firmware 2020.0 LTS to 2023.3 on all supported PLCnext Control devices:

If subscribing to multiple matrices within a single subscription the OPC UA Server does not provide data. However, if only one matrix is subscribed, it works.
If a 2D matrix of type String is subscribed, the variable update of a previously subscribed 2D Int matrix freezes. This condition can only be removed by resubscribing to the 2D Int matrix.

Known for firmware 2020.3, 2020.6 and 2021.0 LTS on all supported PLCnext Control devices:

Due to changes of the OPC UA® server namespace, some OPC UA® clients may cause a BadNodeIdUnkown error. The affected OPC UA® clients do not synchronize the namespaces correctly on start-up, resulting in invalid NodeIds; e.g. Visu+ <= v2.54 throwing an -2143420416 error code. 

Visu+ users updating from firmware 2020.0 LTS or 2021.0 LTS are not affected, but updating to or from a feature release (a non-LTS release) will cause this issue.

Remedy: Visu+ users can adjust the namespaces manually as described in this Phoenix Contact Knowledge Base article. User of other affected OPC UA® clients should contact the respective manufacturer.

Known from firmware 2021.0 LTS on all supported PLCnext Control devices:

Starting with firmware 2021.0 LTS, the application URI is checked against the client side certificate. Some clients do not support the application URI so the OPC UA® Server declines a connection; e.g. Visu+ ≤ v2.54 throwing an -2145976320 error code. This issue only comes up when using a PLCnext Engineer template ≥ 2021.0 LTS.

Remedy: Checking the application URI can be disabled in the OPC UA® Server configuration as shown in this Phoenix Contact Knowledge Base article.

Known from firmware 2020.0 LTS on all supported PLCnext Control devices:

If two or more DataLogger sessions are configured to write to the same database, only the data of one session will be transferred to the database on the SD card at the end. The user does not receive a message that not all data can be saved.