Fixed it
Solution: extract Token again from Robot and put it into plugin config.
Background:
Since I did a Wifi-Reset of the Robot, it generates a new Token.
Or since I did cange the Xiomi Server location from China to EU it generates a new Token.
So the Token was invalide and the connection of the openhab plugin did fail.
By the way, all token extration methods via the app, did not work for me.
Token extraction via Backup did work: https://www.youtube.com/watch?v=g4pa7sesTzY