I already opened a support ticket for this, but I'm posting it here too since the forums seem to get more exposure.
Basically, I have a ship (ID 446310) which cannot move. It's on a planet surface, and whether I attempt to cross-terrain, ascend, or move within the city grid I get an error message saying "already travelling". I can undock another ship or vehicle from it and move around just fine, only that one ship is stuck. I can also move on foot too.
It happened when I tried to cross-terrain. When the travel timer reached zero and the page refreshed, I was still where I started off at, and that was when I found that it was now unable to move.