Drawings randomly being filled in automatically by animate, cannot undo

Example; I drew a head, was working on their hair and suddenly the head automatically gets filled in with color despite me working on the hair lineart. I'm confused and hit ctrl z. Nothing happens. It's still black. I try again, and other things are being undone. That gives me hope and endless confusion because on one hand, I'd really like my art to not be destroyed and gone by this random auto fill situation, but on the other I'm lost and confused. Anyway, I provided a video. 

This has happened before and additionally, lines are dissappearing when I draw them on the rare occasion. Say every 30 strokes. I'm lost and I've just updated my drawing tablet's driver, so I should be good on that. I also went through the whole windows ink fiasco so I truly hope that's not the issue. Thanks in advance.