Playing Dragonborn DLC, at the stage of the Summit of Apocrypha quest where I have to use Bend Will to tame Sahrotaar and then ride him.

I can tame and mount him without trouble (which seems to be the part of the quest most people have problems with).

However, while riding him, at the part where you're supposed to direct him to kill two Seekers and a Lurker on a platform as a sort of tutorial for how command mounted dragons, he seems to be incapable of actually killing the three enemies.

I lock on to one of the enemies and command him to attack over and over, and he does, over and over, but they never die. One out of perhaps every 15-20 attacks the targeted enemy's health bar will actually go down somewhat, the rest of the time Sahrotaar's attacks have no discernible effect at all, and in the meantime the enemies regenerate the health lost. Switching from one enemy to another makes no difference. On one attempt he did actually manage to somehow kill one Seeker but that was it - I kept letting him fly around commanding him to attack the other Seeker and Lurker for probably 15 minutes and he didn't appear to harm them in the slightest.

Since all three of the enemies on that platform have to be dead for Sahrotaar to fly on to where Miraak is, the quest is effectively stuck.

Can anyone offer any suggestions on how to resolve this?