Got an odd one. I was refitting my survey ships, and for some reason, although I had two perfectly good survey ships in orbit, the shipyard was refusing to refit them. Yes, one of them had 2 years on her crew clock, but I have refit ships that had crew time on them, and they even rested during construction.
I refit two ships of the exact same class, right before that, but it is refusing to refit two other ships of the same class, even though I have a slip available.