I gave one of my ships a move order, and the blue circle (the one indicating the destination) moved, but the ship graphic did not. This went on for several turns. Symptoms were:
1) The ship behaves normally in all ways EXCEPT that it is now "invisible" because its graphic is back in the position it occupied several turns earlier.
2) The blue destination circle is the only thing that tells me where my ship is located now
3) Clicking on the original graphic (the one that doesn't move with the ship anymore) has no effect. You have to click on the real location of the now invisible ship to select it, OR use the Find button if the ship is not on autopilot.
Saving the game, quitting and reloading DOES fix the problem.
- Proud Canadian