H4- Reclaimer, Utterly broken

Me and my gf were playing local COOP when we killed the Lich. So when it goes to crash we look up and its still floating there. Ok, weird, I mentioned it was meant to explode to her and then we got back in the wraith I had stole and drove on, the Mammoth followed us and the dialogue in game continued as normal. Till we got to the tributes and they was completely and utterly missing, the map simply hadent loaded anything past that point. We got back on the mammoth and it drove on, floating on air untill we got to the parking point for it, where it promptly turned invisible. I then reset the mission by save quitting and reloading. It`s worth noting the walls of the mammoth and floors still seemed to be there, and Lasky still talked about the blockage and proceeding on foot.

Any idea why it broke? I can get the footage if you like?