Homematic Things went offline after some minutes, have to restart homegear


I setup openHAB2 on a Raspberry 3 with homegear and a CUL to control my Homematic thermostats. Everything worked fine for some days and I was able to change what I want using PaperUI. Unfortunately since yesterday the Things went offline with a “communication_error” and I have to restart home gear to bring it back to life. This works for some minutes and than the Things went offline again. Any idea what the problem could be? I was not successful to find a solution in the forum and the log files didn’t say anything to me as a layman…

Would be happy if someone knows what it could be!
Best, Sebastian