Scrollbars/scrollbox corrupted

Out of the blue my scrollbars are suddenly broken and I didn’t even touch the related BPs!

They show up totally fine in the editor but when I hit play this is how they look:

They are now vertical smaller than the sizebox they are inside. What is inside is cropped (less elements visible). The scrollbar shows as full (it signs everything is is visible)

When I create a new scrollbar, clean in the canvas and scale it very long vertical it is not cropped but is shows the same amount of elements and the bar shows also full. (So it has a few elements and then lots of empty space.)

Any ideas?

I tried changing random settings on them, sometimes it crashes on save, sometimes it crashes on compile. Nothing fixes the corrupted behaviour.