Openhab stopped working for unknown reason


I have been running OpenHAB 2 on a RasperryPi (OpenhabianPi) for several years. Suddenly, my home automation did not work anymore. At first, I tried restarting my Rasperry Pi. Restart itself works, the system comes up again and login is possible. However, the OpenHAB services are not running, e.g. the services openhab logviewer and PaperUI are not running.

When I check the OpenHAB status with
sudo systemctl status openhab2.service
I get the following error:

● openhab2.service - openHAB 2 - empowering the smart home
Loaded: loaded (/usr/lib/systemd/system/openhab2.service; enabled; vendor preset: enabled)
Drop-In: /etc/systemd/system/openhab2.service.d
Active: activating (start-post) (Result: exit-code) since Sun 2023-10-08 09:58:53 CEST; 42s ago
Docs: Introduction | openHAB
Process: 957 ExecStop=/usr/share/openhab2/runtime/bin/karaf stop (code=exited, status=1/FAILURE)
Process: 944 ExecStartPost=/bin/bash -c /usr/bin/find ${OPENHAB_CONF} -name “.x" -exec /usr/bin/rename.ul .x .rules {} ; (code=ex
Process: 989 ExecStart=/usr/share/openhab2/runtime/bin/karaf ${OPENHAB_STARTMODE} (code=exited, status=1/FAILURE)
Process: 977 ExecStartPre=/bin/bash -c /usr/bin/find ${OPENHAB_CONF} -name "
.rules” -exec /usr/bin/rename.ul .rules .x {} ; (code
Main PID: 989 (code=exited, status=1/FAILURE); Control PID: 990 (sleep)
Tasks: 1 (limit: 4915)
CGroup: /system.slice/openhab2.service
└─990 /bin/sleep 120

Oct 08 09:58:53 openHABianPi systemd[1]: Starting openHAB 2 - empowering the smart home…
Oct 08 09:58:53 openHABianPi systemd[1]: openhab2.service: Main process exited, code=exited, status=1/FAILURE

How do I go on from here to find out what the actual problem is? Or is that already clear from that error?

Thanks a lot, Torsten

check with

sudo journalctl

and the content of /var/log/openhab/openhab.log resp. the log file in /var/log/openhab2/