The appearance of the Google Play or Game Center sign-in notification that appears when you launch the app does not indicate that your account has been successfully linked.
In order to link your game account to your Google Play or Apple Game Center account, go to Menu > Account Transfer.
Please refer to the following steps in the FAQ to link your account.
*The option to connect to Google Play or Game Center may not appear depending on your app settings.
Please note that your app data cannot be recovered if you have not saved any account transfer settings prior to deleting the app.