Low step count when activity is golf

The last two times I have played golf, the watch has not been counting my steps. This morning, I had a step count of over 14000. However, despite walking 9km around my golf club, my step count is only 18000, while my phone is showing 26000. 

As I said, this is the second time I have noticed this, and it could be related to adding the Approach T10 sensors, as I added 3 the last time I played.

Damion