Hi,
I was experiencing the exact same issues and I finally managed to make it work.
Issue:
1) I was sending -to my friends owning Apple Watch- activity share requests. Although they were accepting my requests, they were always displayed as pending in the sharing tab of my iPhone's activity app.
2) When I was sent Activity share requests, although I was accepting them I could never see my friends' activity (or for a very short amount of time before it was disappearing and seen again as a share request). My friends, however, would see my activity.
I unpaired and paired my Apple Watch many, (hard) rebooted it, rebooted my iPhone, reset it to factory settings many times without success.
It turns out that the issue was a iCloud related issue.
Back in the day I was a .Mac, then a MobileMe user and was logged into my iPhone with my
@Mac address and with my
@me address for both FaceTime and iMessage.
To fix the issue, I logged out of my Apple ID (
@Mac), FaceTime (
@me) and iMessage (
@me) on my iPhone. I then logged back in using the
@icloud alias of my Apple ID and -boum- it worked.
All my Friends shared activity now show up properly on both my iPhone and my Apple Watch.
My devices are an iPhone 7 Plus (iOS 10.2 beta 3) and an Apple Watch Serie 2 (Nike) (watchOS 3.1.1 beta).
Hope this help.