The GPS is part of the modem, so it does not appear as a separate USB device. There is a separate USB interface for the NMEA port. That appears on the connections management page (CC3G web interface homepage -> management -> connections) when GPS is active.
The “NMEA GPS Processor” line should only disappear if the user kills or disables GPS.
It is very helpful to run a trace while the problem is occuring. Ideally start the trace before the GPS problem occurs, then reproduce it. To capture the trace, open a telnet session to the device, save the output to a file, enter this command:
set trace state=on mask=modem:+cwi,usb:-*,chat:*,ppp:*,address:*,gps:*
Jun 19, 2019