I'm preparing my set for this Saturday and I've just had the same weird thing happen twice which has never happened before.
Basically a clip (it's happened with different ones) is selected and after playing once the output flashes white once before freezing my mac. While trying to resolve this by clicking on things the main modul8 interface turned black and then the output image split into squares like a badly assembled puzzle.
There's no possibility of force quiting and a reboot was the only solution.
Any clues?