I have the same problem.
With the senor GSC10 the unit is working perfectly.
The magnet-less sensors are ok (the green led blinked when you installed them), but when you ask the unit to scan for sensor nothing will be found!
I have also reseted the unit. Nothing to do.
Any suggestion?
Go to Settings->Bike Settings->bike name->ANT+ Spd/Cad->Sensor Details.
You will find a list of 4 check boxes.
Select “Spd Sensor” or “Spd and Cad Sensor”. “Spd/Cad Sensor” is for a combined sensor like the GSC10.