Plesk panel empty ? while sites are working

Hi, I'm using latest 12.5 build of plesk (Web Pro edition) on Debian 8.
Until now it was working like it should.

When I changed to Power User view, a got to the login screen, after login in as root, I'm seeing that everything is gone ? I'm getting like a first setup page :


I have 5 domains on this server, that are accessible without problems.
But the backend seems to be gone?
Is there anything I can do about it? should I restart Plesk to...

Plesk panel empty ? while sites are working