To teleport an entity between dimensions, the server makes a copy
and puts the copy in the new location, and marks the old one dead.
If this method got called for the same world in the same tick,
the entity would not have been removed from the UUID map, and the
world readd would fail.
This can be triggered even with a plugin if the entity is teleported
twice in the same tick, from world A to B, then back from B to A.
The re-add to A will fail to add the entity to the world. It will
actually be there, but it will not be visible on the client until
the server is restarted to re-try the add to world process again.
This bug was unlikely to be seen by many due to the double teleport
requirement, but plugins (such as my own) use this method to
trigger a "reload" of the entity on the client.
Aikar