I don't mean lag in multiplayer, I mean during single player with AI "bots" if you will.
 
I was playing a game of Rocket Race on the big 4 player map and things were going fine all four teams had huge masses of Darwinians (which are totally cool btw) and I thought to myself how groovy it looked when these massive armies of 2D shapes clashed, but at the same time thought maybe I would experience a crash due to the large amount of units being used. However I had heard there was a cap to the amount of units in play at any one time and so naturally assumed it'd be fine. 
 
About 10 minutes in however the game literally started chugging along at 2 frames per second no gentle slowdown it just suddenly dropped to 2FPs. Had to turn the xbox off, haven't tried another match of RR yet and I hope it was a one off because its a really neat game. 
 
Anyone else experience this or a similar problem?