You are right, after a few hours after reset the problem re-appear.
I reboot my Apple Watch, this method works for a few hours and then it stopped. The problem re-appear again.
After a reboot I turned on the Airplane Mode on my Apple Watch so that it can disconnect from the iPhone, and works, then I turned it off. Once both iPhone and Apple Watch are connected again, the app automatically syncs with all the latest information, but after a few hours the problem te-appear again.
I am using my Apple Watch on Airplane mode and I sync one time per day with Health and Activity apps, and after synchronized, I turn on the Airplane Mode again, to avoid the problem.
I have Apple Care, but I don’t think they can solve the problem, and I agree with you that replace the Apple Watch will not solve the issue.
Did your problem starts after the upgrade to IOS 11.2 and watchOS 4.2? Mine start after that.
Do you have any sleep app installed?
I have iPhone 7 Plus and Apple Watch serie 3.