Duplicate distances can sometimes occur when:
Your accidentally submit the same distance twice. This can happen pretty easily when you hit the submit button again.
Two apps that you are connected to both send us the same distance. This is usually when you have something like Strava sending a distance to Google Fit, which then sends it on to us, and then Strava also sends it to us. Best to disconnect one of them.
You can delete duplicate entries by:
App
Go to the "Newsfeed" tab on the right drop down menu
In the filters section at the top. Select "Just Me" and "Distance"
This will show all of your distances.
From the list of distances, find the one you want to delete and click the little x in the top right corner of the distance entry.
Web
From the mission page click on the "My Newsfeed" tab (Green tab)
In the filters section near the top. Select "My Activity" and "Distances"
This will show all of your distances.
From the list of distances, find the one you want to delete and click the little x in the top right corner of the distance entry.
Both the person whose distance it is AND the mission admin (of a group mission) can delete a distance.
Hope this helps!