Sensor status unavailable with homeMatic IP Cloud

I use homeassistant with the homematicIP Cloud integration (64 devices, 152 entities).
Usually it runs fine. But now and than some entities show up the status ‘unavailable’ or ‘none’ or ‘unknown’. I did not find anything in documentation about this states. What could be the reason for this behaviour and how could I avoid it?
I do a system-reboot to have all sensor states available again.
Raspberry 4
homeassistant 0.116.0