When I started up my game today and played it was the same for me after it was working fine last night.. I just rebooted my computer and restarted the game and it was ok. I would include my logs but it look like a few have already done that.
It seems to be a problem with initialization, never starts in the middle of a battle and I have never tried to play more thatn one battle like that, usually goes away after a reboot.