dlinear:
Actually, pulling out the USB cable was the main method I used to fix it before I discovered I could restart the computer.
You pulled out the cable to fix a problem, not cause it. Did you actually read that thread?
I believe this implies something isn't right in the usbser.sys driver since XP. Another link I posted implied this problem went away when using a XP machine.
That is the very definition of "specious reasoning": There is a problem with usbser.sys (low speed bulk transfer; whatever that is) so that must be what is causing communications to stop in my case (even though the symptoms are clearly not the same).
Less noise would be better, but I can't guarantee the noise levels in the background when I deliver this instrument.
Of course you can. Keep electrically noisy things away from signal lines. Shield signal lines. Use a physical layer that is more immune to noise.
While it could be true that the many cables I tried were inadequate, I don't believe this explains why the problem goes away when I use the USB 2.0 hub instead of the USB 3.0 hub (unless the two USB 3.0 A->B cables I have are also bad).
The USB 3.0 HUB lacks proper shielding?
The arduino cable is already very short at 18".
One inch is short. 18 inches is an antenna.