Inspire 3 won't track my active zone minutes accurately

[nms1]

I walk my dog every day. Mon-Sat for 35 - 40 mins, Sunday for. 50 - 60 mins walking at the same pace. On Mon - Sat I will log 30 - 35 active zone mins but on Sundays I will log a lot less. Today, for example, I walked for 55 mins with only 37 mins in the active zone.

The only difference is that on Mon - Sat I shower and eat breakfast first but on Sundays I go straight out to walk. 

Any ideas why? 

It's very annoying as this is my only exercise on Sundays so, despite walking for close to an hour, I rarely hit my 50 active zone target. 

Moderator Edit: Clarified subject

[Gr4ndp4]

Hi, @nms1, welcome, you may be interested in this article What are Active Zone Minutes or active minutes on my Fitbit device? I apologise if you've seen it already.

One of the links above takes you to a description of HR tracking.

I know others in the community are much more knowledgeable than I am on HR and what might affect it. On Sunday you do not have breakfast, your HR on weekdays might be affected by just what you consumed before setting out (Coffee for instance). Alternatively, you may have consumed something on Saturday night.

Cheers

[nms1]

I can only think that it is breakfast that makes the difference, although I don't drink anything with caffeine. And this happens every Sunday so I don't think it can be related to anything I eat on Saturday evening.