|Adding more details and re-reporting this bug: http://us.battle.net/d3/en/forum/topic/6934726311|
[Details]: When playing Act II mission - Lair of the Witch, on the Boss fight with Magdha, the game lags severely that it will actually cause in-game death for a well geared character fighting a relatively easy boss-fight.
The game then resumes acceptable frame-rate (FPS) after porting back to town, and returning to the lair (when boss-monster is dead).
Since there are multiple people reporting this, this isn't user side issue. I have a high-end hardware, and my ISP is showing good MBPS. This is a game system issue that could be happening behind the codes of the Magdha boss fight.
Additional notes: After dying, fighting Magdha the second time and repeating the process makes the lag appear only a third as terrible.
Number of Repros: 3
Bug severity: High
Bug Type: System
Thanks for your reports. This bug actually is not related to your computers, but a bug within the Maghda arena. There is a specific sound file that is producing an error over and over, spamming the client with this error message. This is only happening in the Maghda arena, and will be fixed in an upcoming patch.
I'll update the Known Issues as well now that I know the cause of this.