Garmin tells me I’ve ran 307.6 miles so far this year yet only 299.4 miles are counting towards the 2021 challenge. The discrepancy varies regularly from 1.4 to 8.2 miles short. I’ve updated everything and synced to my pc to no avail.
Sorry I can’t seem to share the lin
Either click the Share symbol on the app screen (the one right of the camera symbol), and select Share as Weblink, or open the Activity in Garmin Connect Web, and share it from there, or post the address line of that page (you'll need to make the Activity visible to Everyone by selecting the respective option after clicking the padlock symbol)
OK, well, I do not see anything suspicious on the activity, except perhaps that it tells "Summary Data: Edited", though normally it is not a problem.
In your place, I would try the following:
When you find out, post the result here. If the distance is always reduced, then you'll probably have to contact the Customer Support and have them investigating it. If so, please then post the conclusion here, for others who should encounter the same problem.