I’ve come across a story breaking bug involving the Sylvari Vigil story quest. It’s the one of the three choices given when dealing with Mazdak. Near the entrance to the Ascalon Settlement, a Risen Thrall spawns in the air, near the big banner-like object. It cannot move, and attacking it will trigger the invulnerable status. The part where it gets story breaking is when reporting back to Branthyn after completing the final objective, who will be endlessly attacking the Risen Thrall, making it impossible to start dialogue with her. It happened to me twice in a row, so I believe it’s repeatable.
