Ok, was worth a shot. On Android there is similarly Google Play games and experienced same described behavior when game wasn't connected\logged in as shown under in game settings.Yes, I'm logged into Game Center. Unfortunately Game Center on iOS does not store the progress of the game, it's only keeping an info about some vague 'levels' (trophies/ milestones/ goals) achieved in the game.
Same here @dr_fly – I suppose that the databases of our games are corrupt and G! won't do anything with it.So I took a backup of my iPad and wiped it... re-added the game.
So my game is currently at 850 MB.
But the issue with the slowness and hanging is still there.