Activity minutes on series 6 Apple watch

Hi,

I recently purchased a series 6 Apple Watch for my partner, it seems to be working fine apart from when we track a walk. We will walk for 35/40 mins, my series 4 Apple Watch will log all the minutes as active time, but the series 6 will log 3/7 minutes active time. Is anyone else having this issue. When we go in the app on the phone it has a full gps route we have walked and heart rate etc but will only close 7 minutes of the activity ring.

any ideas?