Skyrim Special Edition 2020-10-26 16-29-00.mp4
It looks hilarious but I don't know what causes it.
edit: The bug is gone now, I tried removing the npc's outfit, disable/enable npc, played a scene as a test then it was gone. Also rolling back to an earlier save works.
I think it was just some script lag not too sure as I don't know how to recreate this bug.