Hi
If Activity data is changing on your Apple Watch after initially being recorded, then, whilst I can't say why that is happening, the following steps may help:
If you are sharing an Apple ID with another user, then stop doing so.
- For Activity tracking and reporting and various other features and services to work as intended, each person should each have a separate Apple ID and be signed in accordingly on their own devices.
If you have not yet done so, then update your iPhone and Apple Watch with any available software updates, starting with your iPhone (begin by making a backup):
On your iPhone, go to: Settings > Privacy > Motion & Fitness - check that both Fitness Tracking and Health are enabled.
On your iPhone, in the Watch app, go to: My Watch > Privacy > check that both Fitness Tracking and Heart Rate are enabled.
Close certain apps and then restart (normally) both your iPhone and your Apple Watch:
- Turn both devices off together, then restart your iPhone first:
If you are using any third-party fitness, sleep or heart rate tracking apps, check the developers' support resources and/or contact the developers to check for any known issues affecting how data is shared to the Health app on your iPhone and reflected within the Activity app on your Apple Watch.
Check and, if required, adjust the priority order of your data sources for Active Energy:
Unpair and re-pair your Apple Watch:
If the issue persists, then I suggest that you contact Apple Support (remote diagnostics and/or mail-in service may be available, if required), make a Genius Bar reservation or visit an Apple Authorised Service Provider for assistance: