Staff disappears if a note/rest on it is dragged upwards significantly

To correct the nomenclature, the "note" you pointed to in the screenshots is actually a "rest", and the "note string" is a "staff" or "stave".

An easier way to describe this issue is, take the default score and select the rest in the first measure, then set the y offset to -150.00sp, then continue to click it down. You'll see the first staff moving slowly out of sight, because there's not enough space to show both the rest and the staff on the same page.

But what's the point of fixing this "issue"? Do you have a real-world use case of moving something so far up away from the staff?

Identical report was made at #311524: The note disappears behind the note page if drag&drop note down

It is kinda the opposite :) But sure, the "issue" is the same

MuseScore is moving things because notes are being dragged around. It's just moving in different directions when you drag the note in a different direction. It's by design and there is no need to drag a rest off the screen because you don't want it in the staff. Just make it invisible.

I realized people were doing this when the switch from version 2 to version 3 came along and version 2 scores that were imported showed these bad results. In version 2 it was mostly harmless because the systems didn't avoid these rests. In version 3 there were 70 space gaps between staves and the rests became visible, especially in continuous view.

Ah, I guess that's why some scores from MuseScore 2 I downloaded from musescore.com look very weird in MuseScore 3!