Summary: Game will freeze while hosting game online during autosaving.
It happened most consistently in Act 1 Inferno Hard. I do not think it happened every autosave, but at least 1 out of 4 autosaves. If I was hosting the game with one other player, my game froze on autosaving during gameplay. Then when I reset my system, rejoined the game now hosted by the other player, they froze while autosaving. I hope this info helps.