Tacx NEO Bike speed difference between app and fenix 6 pro

Hi,

I noticed a strange difference between the speed metric shown on the Tacx App and the Fenix 6 pro. While I do a workout and tracking both on the app and Fenix 6 pro it looks like most metric are the same, like RPM, Watt, BPM (via Garmin HRM)… but for some reason the speed (km/h) is 1,5-2,5 lower on the Fenix!?

Anyone a suggestion on the root cause?

thanx, Co