Can´t edit forms anymore

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Hi, today I realized that I can´t edit forms anymore. The popup says "Bearbeiten" (Edit), but the rest is blank. No problems with text editing.

I get this error:
ReferenceError: Can't find variable: miniSurvey
initFormBlockWhenReady

Does anyone know what this could be? I´m using Concrete5 5.6.3.1, so maybe an update would help?
Thanks, Philipp