Zone activity not registered even though motion detected

Hi there
I have discover what I think must be a fault in the zone activity handling.
In my hallway zone I have a sub zone, called ‘motion sensors’ in which I have my two motion sensors (hue) turning on the lights. What I found is that even though the motion sensor detects motion the sub zone does not always become active = lights does not turn on!

Anyone else who noticed this?

Regards Allan