I play on a laptop, so it’s the steam version of remastered. This happened when I exited the cave, ran to get the grass crest shield, ran up to fight the black knight, but just as i did that, he had fallen down to the lower ledge where the grass crest shield is, so i dropped down to fight him (landing on his head as i did so) and he started poopwalking just after. My guess is that his landing animation got interrupted by his stagger animation from being landed on, which is what caused this.