That is really strange! I will have to dive into this to find a possible issue.
Is this with other npcs aswell?
EDIT: Found the issue. checking the isStunned function is done by checking the players height, when having a staff equipped like your player it throws of the whole isStunnd function as the height of the stun animation is almost identical to the player height witht eh staff.
I will add some thing for this. thanks for the video!