"Server has been shut down" message for admin login after update docker CODE


I updated my docker hosted COCS to the latest version and now getting the Message “The server has been shut down” after entering credentials. I can see the GUI in the background but the message which has no OK button to dismiss is overlaying.
Integration in nextcloud works fine.

Any ideas how to get rid of this message?

It used to work before and beside of the update I have not changed anything.

I use apache2 as reverse proxy with the documented settings.