Trying to Undo brush layers of the "Paint" effect - strokes not disappearing

I am painting over lines in my video in After Effects and for some reason halfway through my project I realized that I suddenly lost the ability to undo brush strokes when I made mistake. I pressed Ctrl-Z and the brush stroke didn't delete! I keep pressing undo (the menu says Edit-> "Undo Stroke") but nothing happens. When I open the effect in the timeline on my layer, I can see the brush strokes deleting layer by later when I Undo, but nothing changes on the screen until I hit the last layer when the menu says "Edit -> Undo Apply Paint Effect" and once I do that, every stroke deletes all at once. It's super frustrating that it was working and suddenly stopped. Hoping someone has an answer for this!