I found a rare (blue) pack of Dark Hellions in Halls of Agony Level 2, and killed the pack, but one of them is now untargetable and taking no damage/cc. I can’t change skills or teleport to town because it constantly hits me (and is doing actual damage).
On season softcore.
Some additional details - When I zoned in to another zone via a doorway, the rare did not follow me. However, when I zoned back in to the same zone via the same doorway, he was still there and would immediately attack me again.
I came in from the waypoint next, and when I got back to where the rare was, it again resumed attacking me.