No.

The problem started out "soft" -- some things worked, others didn't, over a period of an hour or so after which nothing worked that was connected to the four USB-3 ports n the backplane. I rebooted many times, usually a cold reboot, occasionally a restart, with the computer itself both warm and cold (I turn it off overnight). I tested with several devices (Kindle, iPod, two different mice (mouses?), scanner, and the two USB hubs themselves) and even replaced the two hubs, thinking they may have been the problem. Nothing worked... until the computer went to the repair shop at which point it began working perfectly, and has been doing so ever since.

tanstaafl.