Hello rayjaynj,
Thank you for using Apple Support Communities.
I understand that the Reminders on your Apple Watch are not syncing with the Reminders app on your iPhone. You have done some good troubleshooting already, but one additional thing you can try is to check your Notifications and settings for it. See this:
Choose which notifications you get
You can customize the notifications for each app that you use with your Apple Watch. By default, your Apple Watch notifications mirror your iPhone settings. For example, if you set your iPhone Mail app to notify you only of VIP emails and your watch notifications mirror your iPhone, you'll see only VIP email notifications on your Apple Watch.
Check out this article: Notifications on your Apple Watch
"For built-in apps, you can choose which notifications you get:
- Open the Apple Watch app on your iPhone.
- Tap the My Watch tab, then tap Notifications.
- Tap an app. If you want the app's notification settings to mirror settings on your iPhone, tap Mirror my iPhone. If you want to choose certain types of notifications to get on just your Apple Watch, tap Custom.
For third-party apps, you can turn off notifications. Scroll down to the Mirror iPhone Alerts From section and turn off the setting next to the app."
For Reminders, open the Watch app on your iPhone. Go to Notifications > Reminders. Select Mirror my iPhone.
Setup a test notification to test out if they're working as they used to.
Best regards.