This happens on machines that are below minimum specifications, specifically single-core machines. The game manages a ton of animation, and the second core is used to process all of that data. Without the second core, everyone in-game just becomes a pile on the ground. The only fix for this is to run the game on a machine that meets the minimum specs - namely dual core or higher. If you're machine is dual core and you're still experiencing this problem, check to be sure that your computer isn't forcing single-core when you run the game.
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