I also have the exact same issue.
I have tried now with iOS 13.2 beta 1, and Watch OS 6.1 beta 2:
- Wipe my Apple Watch 5 completely from the Apple Watch app
- Remove all Watch devices from Health (there were two)
- Remove my Apple Watch from iCloud devices
- Restart the iPhone 11
- Then pair the Watch 5 again with the iPhone 11
- Result? Two watches in Apple Health - one that is "not paired" but still receives all activity data, and one that is paired but has no data
Also, if I rename my Apple Watch in the Apple Watch app, nothing happens in the Health app, even if the app is restarted. However if I restart the iPhone after renaming the Apple Watch, only the paired watch gets renamed, but that has no data at all.
This **** happens during setup of the watch. If I open the Health app during the pairing process, at first only one watch device is visible. Then something happens during the setup that causes the ID of the watch to change which causes the Health app to produce a double post of the watch.
So something is very wrong in the Apple Health app, even in the latest 13.2 beta 1 released yesterday.
The crappy thing is that IF they fix it, the correct fix would probably to allow all NEW data to flow into the paired watch. Which means that if you remove the non-paired device in the list all your data will be gone... What a mess...