The first time I tried to play this instance Trahearne was fine. We escorted the teams to the southern exit, he called his minions, we fought our way out of the cave. Then during the cinematic coming out of the cave I was disconnected.
Since then I've tried several times, but I'm having a different issue now. After fending off the undead horde and watching the cutscene with the first research team Trahearne disappears from the instance. I tried several times, but without him following the conversation and cutscene with him at the southern exit won't trigger.