When I enter the Southern Highlands in act 1, or a certain area of the Halls of Agony, something happens and my FPS when monsters are around will drop to 10 or lower. This will continue to happen until I restart the game.

The FPS drop happens every single time I enter the Southern Highlands, as soon as I enter. On the other hand, I can do all of act 3 and act 4 without my FPS dropping below 60.

Interestingly, I figured out that if I have one of the hulking things in the Halls of Agony kill me by throwing me off the edge, this will 'fix' the bug and my FPS will return to 60.

Is anyone else experiencing this?