Wrong distance and speed

In my last 3 rides my K2 recorded incorrect speed, also the Average Speed and Distance were visibly incorrect. Yesterday by about 2 km/h and 7 km respectively (20 km/h instead of 22 km/h for 57 km instead of 64 kilometers). I recreated the route in Strava's route builder, which confirmed a total distance of 64 kilometers. My ride time was 2h 47min minutes.  My partner's recordings, who has also a K2, seem to be correct (see screenshot below)

I am using a Garmin v2 speed sensor with a fresh battery on 700c wheels with 30mm tires. 

Could someone from HH please respond?