Speed Drop-outs During Activity

Hi All,

Can't see any recent posts on this so wondering if anyone is having the same issue.

I have a Forerunner 935 I use for kayaking. When I look at my speed chart after an activity it is a combination of recorded speed and zero's, like micro GPS dropouts every couple of seconds. Rather than a constant line. Settings are GPS & Glonass recording every second. Kayaking profile. GPS reception is strong at the start and always green before hitting go. The experience is consistent throughout the activity.