White Page after Update


Network license
License owner
I did a manual ftp update from 3.12.10 to 3.13.0
I uploaded all files tow times, so i think its not a problem af missing files.
I also did another chevereto update on a second site, on the same server without an problems.
Debug on the app/settings.php is set to 1, but i didnt get any error warnings.
It looks like an header related problem to me, because the menu buttons inside the dashboard, are also dead.
I am runing: PHP 5.6.40 and MySQL: 5.5.59
My Site is:

Did anyone has a suggestion or idea where i should start to search?

Thank you very much.