A complete PLC shutdown due to OPC UA?

I’ve run into this problem (not for the first time) where my PLC freezes, and the only thing that helps is a reboot.
I found the following in the logs:
runtime.log.1
Sep 22 09:16:26 localhost codesys3: CmpOPCUAStack DEBUG OpcUa_TcpListener_CloseConnection: Error 0x00000000 removing connection 0xb21ef208!
Sep 22 09:16:26 localhost codesys3: CmpOPCUAServer EXCEPTION Unhandled exception in OPC UA server. Please restart the PLC.
Sep 22 09:16:26 localhost codesys3: CmpSupervisor DEBUG Description=Exception occured within the OPC UA Server
Sep 22 09:16:26 localhost codesys3: IoDrvDal DEBUG stops triggering driver-watchdogs; failure info from CmpSupervisor
Sep 22 09:16:26 localhost codesys3: IoDrvDal DEBUG Component ID=0x00000124 is out of order! Vital operation ID=0x00000001 failed!
Sep 22 09:16:26 localhost codesys3: IoDrvDal DEBUG Operation description: ‘Exception occured within the OPC UA Server’
Sep 22 09:38:54 localhost codesys3: IECVisualization DEBUG Visu_PRG: Creating Client for Extern-ID: 2469809092
Sep 22 09:38:54 localhost codesys3: IECVisualization DEBUG Visu_PRG: Creating Client successful for Extern-ID: 2469809092 Returned IEC-ID: 1
Sep 22 09:51:19 localhost codesys3: IECVisualization DEBUG VisuFctCheckForUnusedClients: Removing Client with IEC-ID: 1
Time delta: T#45s985ms Locks: Paintbuffer: TRUE
Sep 22 09:51:19 localhost codesys3: IECVisualization DEBUG VisuFctCheckForUnusedClients: Successfully Removed Client at Address: 2999433664, IEC-ID was: 1, EXT-ID: 2469809092
Sep 22 09:53:22 localhost codesys3: IECVisualization DEBUG Visu_PRG: Creating Client for Extern-ID: 975774383
Sep 22 09:53:22 localhost codesys3: IECVisualization DEBUG Visu_PRG: Creating Client successful for Extern-ID: 975774383 Returned IEC-ID: 1

Wago Ethernet settings status:
Error code: 9
Argument: 5
Unknown blink code 9 / 5
More details about this blink code, refer to the manual of the device.

Has anyone else run into this problem? What should I do?
Maybe I’m looking in the wrong direction? Where should I look if the problem occurs again?

Hi Tomas,
The described symptom resembles one of the problems which has been solved in FW31; what firmware version does your PLC run ?

It’s been working for about a week, and now I’m getting an error.
PLC 750-8212
Version 04.09.01(31)