UUID of Player object differing from actual UUID

I'm currently working on some last minute checks to make sure everything is ready for the big name change opening tonight, and I noticed something weird. When I get the Player object of a player at login, their UUID from Player.getUniqueId() isn't the same as what is shown by the Mojang API. When I try to pull a Player object from the in-game UUID, it succeeds. When I try to pull a Player object from the UUID shown by the Mojang API, the Player object remains null. I have no clue why this is happening and I'm at a total loss for how to proceed when I feel like I can't trust the consistency of UUIDs. Does anybody have any idea why this is happening?

 

@SaxSalute Your server is in offline mode so it won't get the correct UUID from Mojang.

 

Thread locked. Offline mode is not supported.