If you've gone through the other troubleshooting steps for your Apple Watch and are still having syncing issues, the steps below could help. If you try these and still have issues, please contact support.
Check the status of iCloud Calendar
Check that there aren't any recent issues with iCloud Calendar
If you see an issue but it says it has been resolved, the fix may still be in the process of being released (it may take up to an hour to fully resolve)
Turn iCloud Calendar OFF and Back ON
Open the Settings app on your iOS device
Tap your name at the top
Tap iCloud
Turn Calendars
If asked, tap Delete from My iPhone
Wait 5 minutes
Turn Calendars back ON
Restart Devices
Press and hold your watch's side button, and slide Power Off to shut it down
Press and hold the top right button on the side of your iOS device, and slide to shut it down
Press and hold the button on your iOS device again to turn it back on
Once your device is on, press and hold the side button on your watch to turn it back on
Make the Calendar Named 'Sugarmate Readings' your Only Calendar
Open the Calendar app on your iOS device
Tap Calendar at the bottom
Uncheck all of your calendars
Wait 5 minutes
Re-check the calendar named 'Sugarmate Readings' in the ICLOUD section
Wait 5-10 minutes
Turn off all Other Calendars
Open the Settings app on your iOS device
Tap Calendar, then tap Accounts (iOS 14). For <= iOS 13, tap Passwords & Accounts instead
In the ACCOUNTS section, tap each account and turn off: (a) Calendars (b) Reminders (c) Notes
Tap iCloud and turn Calendars back on
Wait 5-10 minutes
If it starts working again, consider turning the above settings back on (one at a time)
Sign out of iCloud and Sign Back in
Open the Settings app on your iOS device
Tap your name at the top
Scroll to the bottom and tap Sign Out
Enter your password if necessary
Restart your phone
Go back to the Settings app, tap your name at the top, and sign back in to iCloud
Reset your Watch's Sync Data
Open the Watch app on your iOS device
Tap General
Tap Reset
Tap Reset Sync Data multiple times (there's no feedback)
Wait 5-10 minutes
Verify Watch Background App Refresh settings
Open the Watch app on your iOS device
Tap General
Tap Background App Refresh
Make sure it is turned ON at the top
Make sure it is turned ON for the Calendar entry below
Verify Low Power Mode is OFF
Open the Settings app on your iOS device
Tap Battery
Make sure Low Power Mode is turned OFF
Check your iCloud Time Zone
In a web browser on your computer:
Sign in to https://www.icloud.com
Click your name in the top right
Click iCloud Settings
Make sure your time zone is set correctly in the top header (where it says Time Zone / Region)
Turn on iCloud Drive
Open the Settings app on your iOS device
Tap your name at the top
Tap iCloud
Make sure iCloud Drive is turned ON. If not, turn it on
Set Time & Date Automatically
Open the Settings app on your iOS device
Tap your name at the top
Tap General
Tap Date & Time
Make sure Set Automatically is turned ON. If not, turn it on
Make sure your time zone is set correctly