i can't get the "the end... again." advancement

I had already killed the ender dragon, I just got an unbreaking 3 elytra, and already had end-game gear, as well as a few ghast tears, eyes of ender, and a LOT of glass lying around, so I decided to go to the end and fight the dragon again, so I did, and I did, and I won, but I got no advancement.