On the latest version although it was also on the previous 1.17.40 it has been noted on several occasions that when exiting a boat the boat can become invisible. If playing two player the additional player can still see the boat. If you sleep for one night the boat usually becomes visible again the following minecraft day. While the boat is invisible I have been unable to return to it in single player mode. In 2 player mode the second player can return to the boat making it visible again for the first player.