I haven't got reliable reproduction steps yet, but I've managed to have it happen 3 times so far.
In multiplayer, while flying the ship, with the compass equipped, I can get into a state where I have the compass equipped AND I am driving the ship AND can (accidentally) press R for compass radial and the ship will become locked in place in the air (without having collided with anything) until ... something happens. I think it frees itself when I get far enough away from it and/or close enough to an island (e.g. by swimming), or both together. The compass radial GUI does not appear.
It does NOT become free by any of these actions:
- removing and replacing the cockpit
- teleporting from the ship back onto the ship
- quitting and reloading the save
- jamming all the keys while driving w/ cockpit (including R)
- turning off all generators and turning them back on
- using Z to full brake and then trying again to move