I've seen the same thing in a solo 1v3 game against the AI (I was the Queen of Thorns, the AI had the Rook, Oak and the Unclean Beast). It happened just as I killed the Rook, don't know if that matters. Like the earlier poster said, the game was "sort of working": I could move the view, change the camera angle, etc. My character icon's animations were still going (the Queen's hair was blowing), but all the action on the battlefield had stopped, as had the background animations (the waterfalls). Also, when I pressed "End Game" to go back to the main menu, I got the "Godlike Demigod" sound clip (presumably related to my kill) after the screen went black.