Also affected by this. On a mac here.
I've noticed that during missions, my FPS will start to drop, followed by a lock up.
Also, any saves from within ground combat, will either load with graphic glitches (blinking rainbow tiles), or, even if its a save on a brand new mission, performance will degrade and game will lock up within a couple of clicks, ~10% of the time might get to end a turn before it happens.