I have searched the forum and found nothing about this. On all of my iOS devices, (iphone 5s and iPad) I am having to login as a guest until the game fully loads then my Gamecenter account kicks in and has me log out and back in again. It is an annoyance to have to log in twice in order to play the game. Please look into fixing this bug. This has only been going on since the last update, so maybe it has something to do with it.