I was attacking a very large stack of Drengi ships with several fleets. (Probably another bug since the AI did not form any fleets--seems like there was 30-ish or more ships in the stack.) After a couple of battles the Drengi ships disappeared from the hex. The ships were still there and I could click on the hex to see them in the info display. I could also attack the "empty" hex and have battles. Once in a while a ship marker would appear in the hex.

The large stack moved into two hexes. One had around 10 or so ships and the remainder in the other hex.  Both of these stacks also periodically disappeared and reappeared as I attacked them over the next few turns.

I was fully scrolled out for the board game look--didn't think to scroll in to see if the issue was only when scrolled out.

I believe this has occurred more than once, but thought I had finished killing all the ships in the hex--they probably had just gone invisible.

--David