Why do I have duplicate workouts in Apple Fitness or Apple Health?

If you’re using your Apple Watch in “With iPhone” mode and you finish on iPhone, make sure to wait for it to communicate with the watch until the watch goes back to the first screen.

If the watch doesn’t have an opportunity to finish, it can’t remove the duplicate workout session (that was used for heart rate).

Alternatively, finish the workout on Apple Watch instead.

Also, if you view the Cadence > History screen, it should detect and delete the duplicate.

Finally, you can also manually swipe left in the Fitness app to delete the duplicate (the one with the circle icon, not the square-ish icon).