There’s no reason that openHAB will ‘discover’ a communication failure until it actually tries to communicate.
I’ve no idea how often it might do that, but will guess most of the time it is just listening for incoming messages and is not worried if none come.
I am suspicious of the time this seems to happen, Do you have automated backups? (including at Fritz) Do you have zwave doing a network heal?
You might turn on debug logging to see if anything else comes out. It’ll make a lot of logs.