His Garmin Connect is much cleaner.
Things went from bad to worse on the 8th when he got a 2nd Garmin, at a guess he's switching bikes and now leaves one Garmin on each. The first problem is that his bike fettler keeps switching the Garmin on on his parked bike, this is creating short track miles away from Miles true location. These appear on Strava and hence UMCA. Second problem is other people joining Miles on a ride and then submitting the track to Miles Stava account (and hence UMCA).
Neither of these problems affect his Garmin account.