I have a new theory, why my thralls don’t teleport down off my walls. All archers positions have stairs that lead downstairs and allow archers to go down if necessary. But they never actually do so. I noticed that when a nearby rotbranch boss attacks my base, the warrior thralls that are closer to the boss and that don’t have a quick way to get downstairs to engage in battle, they run to the nearest to their position stairs. But because of the nearest stairs are pretty far from the boss spawn point, by doing so they move far enough for the boss to get off their attack/chase distance. And after that the thralls simply move back to their position.
Probably this is the case. When the thralls don’t have an option to move, they teleport. But if you give them a ground to move freely, the AI will find the path, will take it, this will give them time to move off the attack/chase distance and won’t trigger the teleport sequence. And the thrall will simply move back to his/her position.
Test this 