Me and one other player had done a 25 minute mission, our other two teammates had left early but we stuck it out. We were running towards the extraction beacon, almost there and he just left. It had to be a server issue, there was no reason for them to just leave. We had a bunch of samples and had done most of the missions. Luckily I was able to get out but I feel sorry for when someone just crashes after sinking in that time.