HR not recorded correctly when I do multiple runs after one another

Hi, I noticed when I do a race that my heart rate is not always recorded correctly. Most of the time my heart rate is accurate. The pattern seems to be when


1) Go into running menu and do 1st workarout, in this case a warm-up

2) After stretching do 2nd workout. The key thing to note is I stay in running menu and do not go back to main menu

3) 3rd workout which is actual race. Again, I start workout from running menu and do not go back to main menu

My heart rate should be extremely high (z4 or z5) but its recorded in z2 range.
I think there is some bug there when you do multiple runs in quick succession. Would really appreciate if you could fix or propose workaround.

I will probably always exit to main menu to see if that helps