I am also having the same problem. You can force the other two side platforms’ events by killing the mobs there, but afterwards it will become stuck again and won’t proceed to the center platform. Restarting instance, re-logging in, restarting client, and repairing the client have had no effect.
Edit: To corroborate some of the other users’ accounts, the symptom of Trahearne speaking only the ending quest dialogue also occurs in my game. See attachment.
