Apple watch changes activities from Strava

Hi there!

I've been facing the following problem: while tracking cycling activities via Strava on Apple watch, it shows inaccurate data in terms of the average speed.

For example, the latest cycling activity:

Strava app: Avg Speed 16.9 km/h

Apple watch activity: Avg Speed 13.1 km/h

Also, for some reason the overall time is different.

Strava counts moving time, and apple watch - elapsed time.

But, in this case, why does the apple watch considers other average speed?

The thing is, it also changes this data after some time. I remember seeing my activity ring closed after I finished the activity, however, after one hour or so the activity ring is not full... what might be the case? Why does it change the activity?

Thank you