First, check if you're connected to the Internet and signed in with the same Game Center / Google Play ID.
If not, try signing in with the Game Center / Google Play ID that you've used when playing Solitaire: Decked Out.
If signing in is not the issue for you, try clearing the cached data and restarting the app.
You can clear your cached data in your device by:
Settings > Application Manager (See More if you can't find it) > Solitaire: Decked Out > Clear Cache
If you can't find a way to clear cached data in your device, deleting and re-installing the app will also clear the cache.
Upon starting the app, check Collection to see that your old progress is syncing.
If not, try winning a game to see a prompt requesting that you choose which data to continue saving.