When Sync is not working ?
Please make sure few things:
1 : You have selected same data storage in both devices, you can check it from:
App Settings >> data storage.
2 : You are using same iCloud id in both devices.
If all things are proper and still persist with same problem then try by restarting your device in which you are facing sync problem.
Please send us email from share feedback so we get all required info from there.
You can get share feedback from: app settings >> share feedback.