Around these coordinates -67143.460938 -123554.679688 5220.901855 the enemy and thrall AI gets wonky. Instead of coming forwards as the player approaches the steps up the skeleton guard will go back and around the long ways to pathfind to the player. Conversely, when coming down the stairs if you command your thrall to attack the skeleton the thrall will take the long, convoluted way around too.
I play SP, Exiled Lands, with no mods.