I've had the 321URX since early March and this has happened to me one time. I was pushing an objective in Battlefield so it happened at the worst possible time too :) No idea what caused it.
I preordered a MPG321URX from B&H on Feb 1 and got it last week. No issues so far. I've been using a 42 C2 for the past year. I've always felt it was a little too big but now I'm having a hard time adjusting down to the 32" size. I do like the increased PPI though.