“My Apple Watch Series 9’s compass is not working, elevation fluctuates wildly (sometimes by thousands of meters), and cardio fitness sometimes records and sometimes doesn’t. Even though I run 7 km and don’t climb a single floor, it still shows 40 or 50 floors climbed.”
[Re-Titled by Moderator]
To rule out a software issue, erase the watch and set it up again as a new device after that.
Unpair and erase your Apple Watch - Apple Support
To make sure that the barometric sensor is working correctly, enable the Water Lock and ring the watch under warm fresh water. Then disable the Water Lock to expel the water from all openings.
How to clean your Apple Watch - Apple Support
Apple Watch Series 9 showing incorrect elevation and floors climbed
