it’s already in FAQ since longgggg time ago, so they don’t do anything at all to fix this.
This just happen to people who have minimum spec PC and only get 30 fps in game. This bug make our fps minus 30, so if you just get 30 fps then your fps will turn to zero, and the game will freeze.
I experience this a lot, and the only solution to fix this is by doing this quest with PARTY. That’s it, do this quest on party, so if you die then the other party member can still finish this quest.
I got through past this by using that method which is PARTY. If you want to do it alone, then I suggest you do this quest after you get to level 120. All this boss attack will miss because your level gap is too big, and after a few minute your computer will get to normal because this boss has finish using that annoying fps killer skill, or you can try to use your lvl 100 pet to kill this boss.