Your other device did not save your Springfield

shadoof07

Force the game to sync your town with the server by tapping the Bart/Millhouse button before you logout or quit the game.

As you stated though, most of the time your progress is not lost when you do see that message.

shadoof07

Cheers! Will try that

adidas4fun68

going to krustyland and back again is a better bet

AirurandoP

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