What does it mean when there is an icon with an exclamation point on it?

The following image shows the icon in the Simon's Slots Lobby:

This icon will appear if your app is out-of-sync with the server.

To remove the icon, you must first press it. This will force a sync of your Simon's Slots progress with the game server. Once the sync has completed, you can resume playing normally. The sync should take only a few seconds.