My issue is basically the same as described here:
https://forums.garmin.com/sports-fitness/healthandwellness/f/vivosmart-5/363581/very-high-kilometers-in-first-second-of-run
but nobody is responding to me there. So here we go:
Lately when I walk or run, a very large distance is often added at the start of the activity (usually around 80km). When I see this happen I usually stop, delete and try again, but today I went on a short run and I didn't notice it, so I ended up with the 50k badge after 30 minutes. Amazing achievement if I may say so myself... I should probably sign up for the Olympics.
It isn't a GPS issue. Wrong readings would show up on the map and it looks fine every time.
I've also exported and analysed the TCX files. The GPS readings are fine, but when this issue occurs the <DistanceMeters> element will contain the wrong value from the first measurement onwards. Also noteworthy is that this value will stay the same during the entire activity. So no distance will be added, but the rest of the readings (hr, pace, cadence, coordinates, etc) continue to be registered just fine.
Seems to me like this is clearly a bug in the software. Under no circumstance should the software add tens of kilometers in the first millisecond and stop at that without throwing an exception. If you can't find the root cause, it should be an easy issue to solve regardless. Just filter out impossible values like that.
Another issue that I've noticed is distance randomly being added to activities. This doesn't happen as often as the issue stated above, but it makes tracking my activities pretty unreliable when I don't notice it. It's usually only about a kilometer that gets added at a time. Upon analysis of the exported TCX, I've found that when this happens, the <Trackpoint> element does not contain a <Position> element. This may indicate that it wasn't able to get a GPS reading at that time. Also an easy bug to fix: No GPS reading = wait for the next one, instead of adding random distance.
Can provide additional information on request.
I believe that even if the root cause would be that the Garmin software gets some wrong data or no data from the phone itself every now and then, it should be fairly straightforward to prevent that from causing issues like these. Do some (better) filtering on the incoming data.
