Why is my progress not synchronised between two devices?
All your progress should be synchronised. However, the workouts will be different on different devices.
If your high scores and history are not synchronised at all between devices, you might have logged in with two different accounts. In that case, log out of Peak on the device that doesn't match your original account, and login again with the login method and details you used to register originally.
Syncing also relies on a stable internet connection and if you are encountering problems then try logging into one device at a time.