I am using OpenHAB together with the homematic binding and it’s working correctly.
However, every time I have a power-failure and OpenHAB as well as the Homematic CCU (CCU3) come up again, Homematic is not working anymore. The root cause is not visible on the web UIs (for OpenHAB, the homematic things are Online and for Homematic, everything is working correctly too) but status changes simply go unnoticed on OpenHAB side. Restarting OpenHAB another time afterwards helps everytime. Looks like OpenHAB only works if the Homematic CCU was started earlier.