Ciao Manfred. Have you allowed Strava to access your health data? You can do it from the menu. The print below is in Italian (sorry for this) but you should choose the field below meteo... try it

You should also give a look to "hidden details" in Privacy. Look if the HR is flagged on

Ciao Vincenzo, 

thanks for the tips. I checked And the settings look OK.

Maybe I should have pointed out that HR is generally visible and that it is only missing in the the overview of my records of a segment as shown below.

Ciao Vincenzo, 

thanks for your suggestions. I checked my settings are correct.

I probably should have mentioned in my post that I do get HR on Strava, but not on some pages (see below).

Hi ​@Manfred,

These are segment efforts, right?

I’ve checked mine for several segments, and it appears that:

• if any (even just one) activity includes running power data, the segments effort overview displays power, as on your screenshot
• if none of the activities includes running power data, the overview displays HR
• this means that you’d need to run through a new-to-you segment (with no previous attempts that included power data) to see HR in the overview 

...in the other words, the running power seems to take precedence, and it doesn't seem to be customisable. If you’d like to have that option, you should submit it as an idea. 

Hi ​@Jana_S,

thanks for your input. I think you are right about this.
A single recording with power meter inadvertently enabled will throw the entire statistics.