I'm running the Mac client also, so I can confirm it's happening to me also. Another guy on the subreddit is experiencing the same problem, so probably just a bug. How often does it happen to you? It's probably once every 3 or 4 hours for me.
first off, i would try to make sure you have to programs running in the background.
it sounds like a hardware issue, lower the settings in game and see if it helps at all. maybe your comp just cant take the strain of the game running at times? if you have stuff like google chrome open; these things take alot of ram.