boat not synced with server

on the survival server im playing on i found a river to spawn,
so i crafted a boat and got stuck in the middle of the river
i didnt know what was going on untill i called an admin
and he said that im sitting in air on his screen, but on my screen i wanst
i got out of the boat and still saw the boat in the same position but again
he said there was nothing there, i wasnt able to get in the boat again
but i was able to walk on it and again on his screen i was standing on air
i relogged and the boat was in another place