Marks post/steps helped me:
- Reboot your Apple Watch before each ride.
- Start Companion App
- Start Zwift
- Unclick the HR square with the Apple Watch connection
- Pick your map, etc and begin
- Before pedaling, hit Menu and go to Pairing
- Click on the HR square and chose your Apple Watch
- Exit to your rider and click the BLE icon in Companion App and pick your Apple Watch