so it can't handle it when you ungroup while isolated in the group you're ungrouping and then try to undo the action. i'm no programmer but what i think the issue is there is it tries to put you back into the isolated group before the ungrouping has been undone, so it's essentially looking to put you in something that doesn't exist and goes mad. i know this, and letting it happen was my blunder. what's not my blunder is that once it did all that it just straight-up deleted stuff from the drawing file, and i checked before doing anything and the outlines of the stuff it deleted could still be selected, so i saved and closed because i didn't remember the last time i'd saved and after doing something weird it becomes really annoying to try and draw in it because it won't preview the image properly and now almost everything i drew is gone and i don't know any way to recover it.