Not enough heart rate data on exercise

[Sandlizard]

When I’m out walking I start the exercise on my Fitbit however when I look at the exercise section for heart rate zones it states not enough heart rate data available.

my Fitbit tracks my heart rate through out the day it’s just on exercise it doesn’t log it.

It’s been doing it the past few days, ive tried restarting and updating but still isn’t working 

[DavideFitbit]

Hi, welcome to the Fitbit Community forums, @Sandlizard. 

Thanks for all the information provided about this inconvenience with your Charge 5. 

It's a bit strange that it's only happening with the exercises. If you haven't done so already, please follow the instructions in this article to improve the accuracy of heart rate information and check the information mentioned here about other factors that could affect your heart rate reading, this has been useful to other users who have experienced something similar. 

In addition, I recommend that you try restarting the device again using the three pulse restart method mentioned here.