What watch model? The watch is a 10. What iPhone model? 16 premix Which exact OS versions? Both the watch and phone have the latest update.
What are the symptoms? The activity rings are grayed out on the phone. It doesn't show an activity on the phone, but it's shown on the watch.
Does the watch still show up as "connected" in BT settings on the phone? I have not checked.
Is the watch connected to WiFi when it happens? Yes.
If the activity rings are grayed out without even a zero count next to them it doesnt have data, lets just conver everything.
Verify bluetooth and wifi are turned on with both devices and they are connected via Bluetooth.
Make sure your devices are not in low power mode.
In the iPhone settings goto Settings>Your Name at the top>iCloud>See all (next to Seed to iCloud)>Health, make sure 'Sync this iPhone' is toggled on.
In iPhone settings goto Settings>Apps>Fitness make sure Live Activities is toggled on
In iPhone settings goto Settings>Privacy & Security>Motion & Fitness make sure the main toggle and health app toggle is turned on.
On the iPhone goto the Watch app. Settings>Privacy make sure Fitness Tracking is toggled on.
On the iPhone goto the Watch app. Settings>Passcode and make sure Wrist Detection is turned on
On the iPhone goto Settings>Privacy & Security>Location Services>System Services and make sure Motion Calibration & Distance is turned on
Goto the Fitness app, tap your picture or initials in the upper right, tap Health Details and make sure everything there is as accurate as possible.
Goto the Health app, find and tap "Steps" under Activities, scroll down to Data Sources & Access. Make sure your current Apple Watch is above your iPhone on the list. If it's not there is an Edit in the upper right you and use to rearrange them (you might have a lot there if you been reseting daily).
A newly paired device will be won't be calibrated for you, this is generally something that happens overtime but if your reseting and pairing the device daily it won't be. Apple has a method to speed the process up.....
https://support.apple.com/en-us/105048