I had a shower thought today about how to make movement work better(?)
Spaceship movement: move the world, not the ship
Player movement: move the player as normal
I don't know if the same solution will work in multiplayer, but it seems each client could have their own world moving around them and the server would have one world that ships move in, instead of moving the server world.
If there are any movement bugs currently, I haven't experienced them. Maybe you don't need to change anything. Great game!