Some background information: I have been battling with a bug since years where chunks wouldn't get loaded when teleporting, whereby the player would get in a basically frozen state. Today I have found out that I have been dealing with a world instance that actually doesn't exist anymore, and thereby causes broken results.

I have been relying on Location#isWorldLoaded() to update my cached Location instance, as I am reloading the world frequently. This method still returns true, even after the world strictly speaking isn't loaded anymore, and I am thereby working with a broken instance.

Location#isWorldLoaded() does basically the following:

return world != null && Bukkit.getWorld(world.getUID()) != null; 

The problem is, that world UUIDs are persistent - they do not change after a reload. This is handled properly within World#equals(Object):

this.getUID() == other.getUID() 

Here, the references are compared (and not the actual matching of the UUIDs), whereby it returns the expected result. Although, I'd suggest comparing the handle, as it otherwise gives a feel of the UUIDs not being persistent (which possibly even lead to the fault with Location#isWorldLoaded()).

The fix, within Location#isWorldLoaded(), could be:

return world != null && world.equals(Bukkit.getWorld(world.getUID()));