Activity green ring not filling while non-workout outside walk or cycle [Apple Watch 2]

I have since solved the problem. Something was seemingly corrupted in the iPhone's Health database. Nothing could read or write data to the Health database, including step data (which should be automatically added from the Mwhatever chip) and manually entered data such as weight.

To solve the issue, I unpaired the phone and watch, then set up both the phone and watch as new. Setting up the phone from a backup did not solve the problem because the (hypothesized) corrupt database was (seemingly) included in the backup.

Since setting up the phone as new and re-pairing the watch, Health data works fine.

Here is another option: In running trails with my Apple Watch and iPhone the calibration is not correct. Miles is not correct because of switch backs and trees. What I do is go to the Watch app on my iPhone, Tap the My Watch tab then tap Privacy > Motion & Fitness > Reset Calibration Data. This erases the calibration and I can start over with a clean slate. You do not have to reset everything using this method.