I don’t know what is causing it, but whenever I attempt the boss battle the game becomes ridiculously laggy, dropping down to 1 FPS or less. Then the game finally crashes after freezing, on top of which the monsters are wailing on you while you are lagged/frozen so a squishier character wouldn’t survive it. This same problem existed during the beta tests, I’m not sure how it still hasn’t been fixed. There shouldn’t be anything causing this much lag in a simple fight against 6 enemies, I fight more enemies than that at one time multiple times a day.
I’m having the same issue! As a mage, it’s impossible for me to move on, the staff should have already solved this, this bug has been on since the open beta last year.