I had that issue with a lot of the imps further into the fjords. What was funny about them is that they would lean on their swords and just grin. I ignored them, retreated, waited a couple minutes then went back, they were back with their group and vulnerable again. In some very rare instances, they would just despawn. I'm thinking a glitch of some sort, but, it made for some amusement in between having my skull bashed in.
