I had the exact thing happen to me, too. The last couple days of this event, the UFO sound has started up, and ends in error each time. I never had that error before this event. Today, it happened quite a bit before I was kicked, but I had been able to complete yesterday’s quest despite it, so I continued on. Just as we got to the steam vents with the Ancient, I was kicked. When I logged back in, I was placed into an overflow that had completed it already.