Same for me with a SSSG AW4 and iPhone X....I lost all sharing on my watch after upgrading from an S3. I called Apple and the issue was escalated to a senior tech who walked me through the same steps most of you have gone through including deleting the activity app and reinstalling. I don’t understand how it could be software related but only happening to a small fraction of S4 owners.
No love, so he replaced the watch which came a week later. Same deal with the new one and haven’t been able to figure it out yet. Bump for others experiencing the same issue...it’s not just you.