Zwift Power misreporting power & w/kg for Alpe du Zwift

Hi All

I rode up Alpe du Zwift the other day as part of FRR in a time of 75m and change (nothing special) at an average of 173W (2.55 w/kg). Zwift power reports my segment as 144W at 2.1 w/kg.

Does anyone have any idea why this might be?