Chamber of Echoes Boss Fight - Boss De-Spawned

The Chamber of Echoes boss fight bugged out for me, after opening sequence, the boss did one attack then de-spawned. This was my first attempt at the fight, no other issues occurred leading up to this. Logging out and going immediately back in doesn't fix the problem. Will have to reset the zone.

I had this happen to me today. No crashes or anything leading up to the boss fight. Started fight and boss despawned after jumping into the water once. Stuck in room, since you can't teleport out. Exited game. :-(