Could be an issue with the temp sensor. It's weird that I've tested seventy of these things and not seen any problem and you've got two of them doing the same thing. Usually when multiple anomalies coincide I start to question the user before I do the hardware.

I'm guessing you power-cycled the miners and the issue persisted, otherwise it'd be barely worth mentioning.

mstrozier - there's no such thing as "too much voltage" unless you're getting too much heat. Set the voltage and let the auto-tune do its thing. If it's not where you want it, step up the voltage and start over. Don't freak out that it's not perfect in ten minutes. Auto-tune can take a couple hours to flatten out.

The USB bus is not connected to the temp sensor at all. That's also why there's no software voltage control. Maybe on the next one.
This is a USB2.0 device but because of the timings and data throughputs required it's fairly sensitive to busy lines, especially without ASICBoost, as has been stated a couple times already.