Exiting the game while being in a boat cause the following issues upon rejoining the game:

1. Boat is invisible or not yet loaded
2. Your standing on something invisible and the boat does not re-materialize
3. If you swim to shore under this scenario and try and place a bed it vanishes from your inventory
4. If you stand on the invisible boat or whatever it now is, sometimes your health bar will drop by 4-6 food levels instantly
5. Sometimes if you want long enough the boat will re-appear and you can play normally.

See video here  https://youtu.be/3s-ZkRdO9hU