Around a third of the time, when trying to exit a boat:

The boat becomes invisible and unbreakable. You can still run into and push the invisible boat around, but not get back in it or otherwise retrieve it.

Additionally, when standing on top of the invisible boat, it is very difficult to move. It takes a considerable jump spamming to get off the boat.

When other players are in the world, they can see and interact with the boat, even if it is invisible to one player.