Some apps use a different calorie model than the one Apple uses. This means that the calories in Activity might be different than what you see after ending a workout. 

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How to solve this

1. On your phone, open the Health app
   
2. Click the 'Browse' tab
   
3. Click 'Activity'
   
4. Select 'Active Energy'
   
5. Scroll down to 'Data Sources & Access'
   
6. Select 'Edit'
   
7. Move the Companion app to the top of the 'Data Sources' list