I'm getting these quick messages about resigning into "GameCenter" that goes away, and I can still play the game like I wasn't disconnected from GLU or Gamecenter. I don't have to resign into GameCenter. I don't have to restart the game. Other than the quick sign in to GameCenter message, there isn't any indication I've been disconnected from anything.
But I do have two registered 'defense lost' entries in my social log an hour ago, which happened while I was still signed on to the game, and two players are happily sharing 13000 diamonds.
GLU: Have you been working with GameCenter today? Change something?
Apple iphone; iOS 7
iPhone 4, usually.