I can confirm that this bug…
“- (Do not have a repro for it) Caith can sometimes fail to become neutral state resulting in her kicking you around the instance (if not selected to accompany you in)”
Is still in effect, I worked my kitten off to get to the end fight but cant finish it because Caith became immune and didnt want to get sucked in to the rift. Once she wasnt stunned anymore she just kicked me around and both she and Mordremoth was immune to damage.