Sense2 - "Not enough heart rate data available" on activity recording

[RolWg]

I have a Pro subscription. The Sense2 correctly measures my heart/pulse data elsewhere. Why do I only get an image with a gray route line in the app for training recording / map / heart zones and above all only the comment: "Not enough heart rate data available"? 

Moderator edit:  updated subject for clarity

[Rich_Laue]

Could you post this image to the thread, or edit your post above? 

Is this "gray line" found on the Sense 2 or the fitbit app? 

What type of stat is displayed on this page? 

Is this the map, or heart rate data

[RolWg]

This is the tab in the FitBit app "Heart Zones" that supposedly doesn't have enough heart rate data available. 

[RolWg]

In many other areas, heart rate etc. are measured and processed without any problems (resting heart rate, current heart rate, heart zones during training). Why not here, where it would make quite a bit of sense?

[JuanFitbit]

@Rich_Laue , Thank you for your help . 

@RolWg ,Nice to see you around. Thank you for your message and sharing the picture. 

It seems that you are using MobileRun to capture your GPS data. 
This feature is though to be used if you were not using the Fitbit while on a Run, Hike, or Walk, and you still want to record your route. 
As the data used is the one tracked with your phone's sensor, no heart rate can be read and recorded. 
To record the GPS data with your Sense 2 please have a look at this: How do I turn on GPS for an exercise on my Fitbit device? and

Built-in GPS

[RolWg]

If the Fitbit app is able to import and process all data from the Fitbit Sense2 - which it is also good at elsewhere with sleep data and heart data - why not here with the combination of running speed and heart rate? Timestamp synchronization shouldn't really be a problem.
Unfortunately, the Sense2 also seems to have much poorer GPS reception than my smartphone with the Fitbit app. The registered path coordinates are much less precise and unfortunately the training tracking also switches itself off when it shouldn't.