Fibaro Universal Door & Window Sensor not triggering

I have multiple Fibaro Universal Door & Window Sensors, all installed fairly easy and all working fine. I have added another one which i just cannot get to work properly. I have replaced the sensor already thinking it was a hardware failure, but that did not solve the problem. Including the sensor was not a problem, but initially it stayed on waiting for wakeup to configure and nothing happened. After quite a few exludes and reincludes, it is finally there without any error message. Initially it come up with waiting for wakeup, but after about 30 minutes that disappeared, and it looks properly included, with the information (capablilities, manufacturer, neighbours) etc all there, and everything except neighbours of course, identical to the working ones. Small problem though, when i open or close the window, i get the blue led flash, but on my Vera the state never changes from green !
I am running out of ideas, and getting fed up including and excluding…

And now the waiting for wakeup to configure has come back… I need a hammer…

Looks as if the fibaro has now decided to report the window being opened or closed. But not all the time. I wonder if it is communication problems. I have a TKB on/off switch socket about 3m away to help comms.
How can i find out if there is a problem communicating from my fibaro ?