Black screen when fighting the Rotten Druid

I keep experiencing this bug while I'm fighting The Rotten Druid. My game screen will just go black. The UI is still visible and I can move around in game. This will happen periodically and after a few seconds or so it will revert to normal.

This has happened to me while fighting the Rotten Druid in Act 1, Act 1 Cruelty, and just now when I encountered him in the Endgame.

It's extremely frustrating. Please fix.