sometimes, usually in big battles with lots of spawns, all of the mobs(and other players if there are any) stop updating and just sit in one place. I can move, but my movement is alternately faster or slower than normal. The game continues to run but I'm stuck like this, unable to see anything that's going on or attack or defend. This continues on usually for about a minute, maybe longer. When the game "catches up" I'm almost certainly dead. Needless to say this is really frustrating, especially when i'm going solo.
