Jupyter Cloud: repeated malfunction rectified

The Jupyter Cloud service was repeatedly disrupted to a limited extent between Fri. and Sat. morning: new logins were no longer possible on the service and a ProxyError was displayed after a certain waiting time.
The entire service with all servers was restarted. All running notebooks were interrupted. All users have to log in again, the running notebooks in browsers have to be reloaded.

The cause has not yet been determined. Unfortunately, the disruption may occur again before the start of regular business hours on Tuesday.