Since updating to 1.10.0, if I was playing Blitz previously and have Blitz as an open app in the background, then go to open it again at a later time, Blitz will not automatically log me into Game Center like it used to with previous versions. I end up getting a screen that want me to login with Facebook, or with a War Gaming account. I have to close Blitz (double click iPhone home button, then swipe the app up and away), and then re-open Blitz to get it to log into my game center account.
So I still can play, but its pretty annoying to have to alway quit the app when I am done playing.
This happens on both my iPad Air 2 as well as my iPhone 5S.