It seems that AI-controlled boats are not initialized properly on dedicated servers.
Sometimes they just sit above the waterline without moving as if simulation is not initialized correctly.
Even with waves at maximum they stand still, and by that i mean their azimuth, relative height or inclination don't change, they stay perfectly horizontal and sometimes their position gets updated following waves, sometimes it doesn't.
When given a waypoint, the AI will attempt to start the engine but the boat won't move anyway.
Then as soon as you swap in driver position the vehicle assumes normal behavior.