Homematic IP things go offline after CCU has been offline

Env.: openHAB 2.5.7 Release Build on Debian (x86 server) - CCU3

I’m using openHAB for 18 months now using mainly standard homematic stuff with a few hmip devices. I noticed that openHAB ceases communication to hmip devices after the CCU cannot be accessed for a short while. I noticed this when rebooting the CCU - but it also happened when exchanging a switch between the running openHAB server and the CCU.

I noticed that there are two posts (here and here) describing this but it seems there was no solution to the original problem. Is there any setting I can fiddle with or is there a way to re-initiate the communication w/o restarting the whole openHAB system (which I would rather like to avoid due to several reasons) ?

Will do more detailed checks if necessary - thanks, Martin

Any thoughts to this problem are very welcome …