Unfortunately, I am having trouble getting my link to stick, but in the same game I uploaded the dead planet problem, more than once I have started an invasion with a troop ship and then added escorts on a later turn (like after they destroyed the shipyard) and the invasion stops and can't restart until the next turn. But, sometimes I could add a ship (especially troop ships) and the invasion would continue. I think it happens when the fleet automatically absorbs the troop ship.
I wouldn't have a problem with the same hex and not protected problem if I knew I could add an escort later. I can live with this, but it seems strange that the fleet just stands by and doesn't help. So, what happens when I or the AI attacks a hex with multiple units? Is the weakest unit attacked, or a random unit. I know from experience it is not the strongest.
Also, in the dead planet link game, later I captured a planet without a capital and I couldn't build a capital. That's the save I haven't been able to upload. It's zipped on Onedrive, but it won't paste. I made this post after 2 days of trying to get capital-less link to stick.