Fenix 5 overestimating hike distance by 25%.

My watch consistently over estimates hike distance by minimum 25%. I know this by measuring on the map and comparing with other Garmin devices in the group. Support have suggested various fixes like GPS soak, software update none of which works. Anyone else had this issue? This is a gross error not minor accuracy suggesting to me this is a repair job not a software glitch. Garmin don't seem very interested in repair.