Hi  , there is no entry in my error log, that's the problem. Some errors in the console, as shown. That's why I would like you to check it by yourself. I cannot find the traces to the error. But the window is empty with a small, framed square in the center.

Edit: Screenshot with Chrome Developer Console attached

access log only shows status 200 entries, except from the una *.js.map files, which I know is common to have 400 error entries for.