Zizek talks about a feature of games where one can sometimes see behind the facade of the created game-world. The ‘reality’ of the game reveals itself to be a flawed, not fully constituted world.
He also explains how incomplete reality is really ultra-realistic, because our own world is not fully consituted. Quantum physics tells us that reality effectively doesn’t exist when its not being observed. This also relates to gnostic theory which says that God is an idiot who bungled creation and underestimated humanity, hence reality is not entirely ‘finished.’
These game glitches represent a collapsing of the illusion of a full and complete reality, and reveal the world in its incompleteness.