Venu 2 plus pace is bouncing around

In the past few workouts when my GPS is on my pace keeps bouncing around significantly. One minute my walking pace can be 17 min then a min later it will show 21min and a few min later it will be 13min. Im coming off a surgery so Im am def not walking a 13 min pace.

I have been using the same route and it is accurate as far as miles recorded.