I've been using the Fenix 7s Sapphire Solar for a few days now, upgrading from an Instinct 2s Solar. I've recorded 8 walks so far and all are 5-10% shorter than they should be (longest walk was 30.2km, resulting in a 27.67km activity). This I checked with another Garmin (FR 255), the planned courses, tracing the route with several mapping tools and by investigating the GPX as exported from Garmin Connect. If one of the activities is exported to GPX and imported again, the distance is correct. The watch seems to be recording data fine, but is not using the actual GPS-data for reporting the distance (and therefore speed). I found some references that it might be that step length is used in the algorithm to calculate distance when GPS data is unreliable, but with this watch I would not expect it to do so.
To be complete, I'm using Auto Select for position, 3D distance and speed, data recording every second, but have experimented with those settings in every setting. I am unable to get the same odd results with the FR 255 or Instinct 2s.
Is there any setting I'm missing here?
