The most common reason why Fitbit miles show twice on the race is that the race is set to collect all activity and you have done a dedicated run or walk. When all activity is selected all of your steps for the day will be sent to the race as well as any steps from a dedicated run or walk. To fix the duplication simply change the activity type to daily activities if you wish to record all of your steps or select running and walking if you only want dedicated steps from runs and walks to pull into the race.
Another reason miles may be showing twice is that the Fitbit is connected to both the old and new Fitbit connections in the tracker section of the app. To disconnect from the old connection:
1. Log into the App
2. Click the hamburger (3 lines in the lower right corner)
3. Click Fitness Tracker
4. Click the GREEN View 3rd Party Integrations button
5. Click the RED x next to Fitbit