I notice this when the enemy NPC encounters some kind of pathing glitch. They can't find their way to you so they just keep trying to move unsuccessfully - I think the game is actually attempting to safe guard with a set time limit on this kind of thing....it's still annoyingly long and it's worse when there is 2 or 3 of them in a big battle - i could brew a pot of coffee before it's my turn again.
