My USB connection is OK, but from time to time some users report a problem...
Reading the thread about "problem" with only 1 channel played in earphones,
it came to my mind, that the chause of both "problems" may be related...
Maybe that some USB plugs are thickier and cannot be properly inserted (because the USB connector is a bit "sinked") and the connection is sort of random.
So, if one experiences random USB problems, it might be good idea to check if the "framing" of the sink does not prevent USB from proper insertion and so causing a loose contact.
It is only my theory based on someone's else experience with an earplug, I do not have such a USB plug.