How Do You Calculate Calories Burned?
If you're recording via Watch, I'm relying on Apple's estimates which combine the heart rate sensor and motion events, and knowledge about you from HealthKit (like age / weight / etc). They put a ton of research into those estimates, so I'm trusting them. To ensure you get calorie estimates via your Watch, make sure your Watch band is tight and you have direct skin contact so it can pick up on your heart rate.
If you record via iPhone I have a more generic algorithm that estimates calories burned based on your time on runs. Note, this does not use the heart rate sensor, so it can't account for how hard you rode like Apple's estimates do.