Apple Watch activity messed up since July

Try these steps:

• On your iPhone in the Watch app, go to: My Watch > General > Wrist Detection - check that this is turned on.
• If Passcode is enabled, check that you are unlocking your watch after placing it on your wrist.
• On your iPhone, in the Watch app, go to: My Watch > Activity - check that Stand Reminders is turned on.

If that does not immediately resolve the issue, next try these steps:

• On your iPhone, in the Watch app, go to: My Watch > Privacy > Motion & Fitness - turn Fitness Tracking off (or turn it on, if it is currently turned off).
• Close all open apps on your iPhone and then restart both devices:
  • On your iPhone: double-click the Home button, then swipe up on each app preview to close each app.
  • Restart both devices, turning both off together, then restarting your iPhone first:
    • Restart your iPhone, iPad, or iPod touch - Apple Support
    • Restart your Apple Watch - Apple Support
• If you turned Fitness Tracking off in step 1, now return to the setting and re-enable it.

If the issue persists, I suggest that you follow up on Apple's recommendation to have your watch checked (under warranty, if eligible). Either contact Apple Support (mail-in service may be available) or make a Genius Bar reservation:

• Contact - Official Apple Support
• https://twitter.com/applesupport
• http://www.apple.com/retail/geniusbar/

To check your warranty status (the serial number is on the back of your watch):

https://checkcoverage.apple.com/

You are most welcome - thank you for your kind words! 🙂