Why doesnt my workout get noticed

[Laurentom]

On days that I go for a 1hr walk, I'm not puffing or tired, and my fitbit acknowledges the workout and the calories burned is around 2k by the end of the day. When I do quite fast paced yoganastics indoors for 1hr I am puffed and tired but my fitbit "ignores" the workout and by the end of the day my total calories burned is low. Why? Is this because every so often I stop to rest/hold pose briefly and my heart rate drops? Or am I really just burning more energy while walking even though it doesnt feel like it?

[JohnnyRow]

There are 2 separate issues here: calorie burn and workout recognition.

Calories burned are based on heart rate.  Whether or not something is recognized as a workout should not affect calories burned.

I assume you are relying on auto-recognition of workouts.  There are a limited number of activities that supposedly can be recognized, based only on the movement pattern of your wrist.  Walking is the one most reliably recognized.  You can see these on phone app by tapping Days of Exercise tile, then the gear icon near top right.

I believe the better way to record workouts is to use the Exercise App.  To get started with that, scroll right from the clock face to Exercise and tap that.

You can read more about that and how to modify the exercise types listed here:

How do I track my workouts with my Fitbit device?