I noticed when the blocks reach that final animation frame, the player falls like 3 pixels in to them. I would bet the stump bug is related to that. Maybe that final animation frame has the wrong sized collision box or something?
I purposefully gave the last frame a smaller hitbox so the player could feel that they are "almost through"... but maybe this should be changed? Open for feedback on this - do you think the blocks should have a full hitbox until they are broken?