If CouchTimes isn't syncing through iCloud, check the following:

• You're signed into iCloud on all devices
• iCloud Drive is enabled in Settings > [your name] > iCloud > iCloud Drive
• CouchTimes syncing is enabled in Settings > [your name] > iCloud > CouchTimes
• Your iCloud account has available storage
• Parental controls or device management aren't restricting iCloud
• Your device has a stable internet connection
• Your device isn't in Low Power Mode

Fixing these issues should restore syncing between your devices.