At the Azj-Kahet location for the Toxins & Pheromones incursion daily quest for Flame’s Radiance, there is a Devourer worm NPC in the shard I was in that has become stuck burrowed in a state that is causing it to immune all attacks. If you enter combat with it and have an attack immuned, you are permanently stuck in combat until you either manage to leave the zone or log out and stay offline for more than a minute.