Nige
I had similar problems, losing the GPS signal feed ?,on reboot,, myself and others tried for hours !! down loaded the Franson GPSGate, (14 day free trail) jobs all cured, finds the receiver, whether via USB or Bluetooth on start up, and can now runs 2 mapping systems, along with a marine chart program, all at the same time,
Do not know the technicalities all i know is that it works