the log file is only filled when I switch the switch via a GUI! (Android app/Basic UI)
When I press the physical button on the “Wall Plug” nothing is visible in the log file
okb (NULL kb) is added to the log file.
Most devices should send reports - if associations are configured - there are only a few very old devices that don’t support this.
ZWave+ makes this easier as it reports these, so the binding can automatically work out what needs to be configured, however if something goes wrong during the initialisation, then this can potentially get skipped.
I would suggest to try and configure the lifeline, or, you can reconfigure the device completely - there is an option to do this in the UI (in the config parameters).
I was facing similar issue. All of a sudden (after more than 10 years) one of my Fibaro Z-Wave Switch stopped reporting item changed and thus my rules were not working any longer.
Finally a “reinitialise the device” in openhab Web UI on the thing solved the issue