This is happening to me as well since the new patch. I have a "pretty" fancy comp that has 16gb of ram and I opened up task manager and im not coming close to the max memory. New patch is hella buggy.
If I restart my computer its alright.
BUT the bigger issue is if you try and queue for a game after this message pops up, my game crashes on start and it doesnt restart the game. When I do get it, the game has already been going and I'm outside the map and have to walk into the main game. It doesn't recognize im not in game at all and starts a game anyways.