I've got version 1 of the Magnetospeed. It has had the issue from day one. The only cable that works from the sensor to the display unit is the thick one. And then, it will only work one way. I had to put a piece of tape on the the end that has to attach to the sensor or nothing works. Should have tried to get them to fix it long long ago...
The connection issue is at the sensor for me. If that connection has not got a good contact, the display won't see it when the cable is connected to the sensor.
I think it is a quality issue with the female plugs on the sensors myself.