This article discusses common toubleshooting steps regarding various problems that might occur while synchronizing sleep data using iCloud:
Recommended steps:
Make sure you have enabled iCloud synching in Pillow:
Open Pillow on your iPhone/iPad > Tap on the Settings icon on the top right corner > Scroll down and make sure "Sync to iCloud" is turned OnCheck the Apple System Status page to make sure there are no outages or scheduled maintenances currently affecting iCloud
Update your computer or device to the latest software version. See iCloud system requirements for more information
Ensure that you are logged in to iCloud with the same Apple ID on all your iOS devices: Open the Settings app > [your name] > iCloud.
Note: If you use the same Apple ID for iCloud as you do for other Apple Services, (for example, Apple Online Store, iTunes Store, or Mac App Store), changing your Apple ID password also changes your password for the other Apple services.