E.g. you`re playing on a tablet or a phone and progress on your phone is not available on your tablet.
In such a situation try to do the following:
1. Ensure that Internet connection is stable. Run the game on your phone.
2. Run the game on your tablet. So basically, the game should be running on both devices.
3. Complete any lvl on your phone.
4. Close the game on your tablet and run it again; download progress from server when asked.
Once you`ve checked through all the steps, progress would be shared between 2 devices.