I've seen this in several of my games so far (and, too be frank, this is crediting me with a lot of unfair wins for myself; my bot tends to win with four leafed clovers and coin flips).
It's happened in four and two player matches, and I have no idea what's happening! One player will just... disappear...? Just that player! Their ships disappear, their planets go unowned, everything! I just thought that the issue shouldn't go unknown about.