Occasionally, boats will leave behind invisible entities that are not intractable with in any way, unless your try to drive another separate boat through the location. It will be treated as if there is a boat there and you will not be able to drive through it.

The entities are not client side, as they are still there for every player involved even when everyone logs off and then back on. The only way it seems to remove them is to unload the chunks and then reload them again.

The most common way i have gotten the invisible boat entities to spawn is by placing a boat half on water and half off, and then driving the boat into the water, then placing another boat in a similar location, and trying to drive through where the other boat went into the water