We've had this same phenomenon, and documented the disparity between the usage at our router (running Gargoyle 1.4.7), at the modem (agrees with the router), and at our Status Meter (overstated). We would like to compare it to the hourly usage level on my.hughesnet.com, but we've had the "OpenID" error there for more than a year, even after multiple tickets about it.
Edit: I see now that sgoshe figured out that his phantom usage wasn't actually phantom. FWIW, our overstated usage only occurs when we have a heavy usage period. E.g., we actually use 500 MB in an hour, and the status meter goes down by 900 MB. This isn't a very chronic issue for us now, as we've slowed the data transfer rate on our router, and try to keep the actual hourly usage from peaking like that. Still, it's an unfair limitation that we need to observe until Hughes acknowledges and addresses the problem.
"Smart" devices using bandwidth. Hopefully HN engineers are smart enough to figure-out how to build an identification mechanism (if only what LAN IP was responsible-for-which Downloads) into their modems, or Hughes will have to hire boatloads of CS and Account Services reps to handle all the customer complaints about "where did my bandwidth go?"
Recently I have been using the Internet to go house-hunting, and have been amazed at all the bandwidth this has used what with Google-Earth (including Streetview) and Virtual Tours.
But the real problem for Hughes is our iPhones and our SmartTVs and media players, not computers...
I just wanted to chime in and see if you had Networx installed on just your PC or if it is installed in your router? Like Glasswire, I am quite sure Networx only detects usage from the device it is installed on, and the only way to read the rest of your network is with the software installed onto the router itself. These programs can be tricky and trying to control/read/understand your entire network from one device may not be the best way to go. Let me know!