I have met now this error for the 3rd or 4th time. After some time of inactivity and when logging in again, I get the famous congratulations screen.
After a restart of the webserver everything looks good again. I first supposed it was just due to updates, but today I didn’t do anything in the settings at all. I logged in in the morning, wanted to log in in the afternoon again and whoops the error screen appeared.
There doesn’t seem to be any error log on the server at least (according to my colleague).