I have a weird problem with the edit block forms, see attachment.
The fields for image and video only show up as a line and not as a input field.
Until a few days back all worked fine and lots of images and videos where entered and/or modified this way.
The problem occurs both in custom blocks as well as in standard Concrete5 blocks, so it might be a Concrete5 issue which I am not aware of.

Installed version is 5.7.5.6
All caching setting are 'off' for development reasons.

Thanks!