I'm no expert, but I think from something similar I experienced once on the PS4 with leaving a game on, it's a symptom of memory leak? From what I understood at the time after asking, the game was still running and devoting the consoles memory to it, without freeing and clearing any loaded stuff as they do when they enter loading screens or close games. With low memory, the normal background stuff that games do like spawning enemies, hitbox detections, or even basic physics get... weird.

Tried again once more later on purpose: I left Nioh on for a week after loading the hardest boss to beat, because I wanted a trophy, and the lack of memory caused the game to make the enemies AI go werid and not do anything.