Here we are many months later - I still get VERY frequently chucked out of the game (attacking is one of the triggers) as 'Amazon app store required'.
I also get the game VERY frequently, spontaneously closing without any error messages. And given signal strength and the issue persisting on many netwroks, it's not intermittent Wifi.
Of course Kindle fire has Amazon App store embedded, so I'm puzzled, and seriously handicapped.
The game is virtually unplayable with these faults! Anyone got news?