There was an unused hell mode challenge where the AI Level is at 20 and all teachers are present. What if there is a feature that makes all teachers hostile at the start of the run? ...or this feature might be in the separate challenge idk.
There is some cases when the teacher's ai may go above 20 and is not hard-capped. And the current difficulty is based on the current challenge selected or playing normal mode. (pure nightmare is 10 difficulty)
Also there is a bug where you wouldn't get hell mode achievement when you get all notebooks wrong in pure nightmare and then exit the school