Your other device did not save your Springfield

Cheers! Will try that

going to krustyland and back again is a better bet

That message is there as a reminder in case you play on more than one device eg: I play on iphone and android tablet. If you switch devices without logging out of the first the game reverts back to the last saved update the last time you did log out.

I experimented with this and the game lost progress I had made on my first device when I logged into the game on the second device.

If you only use one device you can ignore this message no matter how many accounts you have as you have to log out of one to log into another.

Hope this makes sense