Thanks for the reply, Ed.
In order:
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System is fully protected by a 900va UPS. And it’s a 230v system, currently at 227v. Log shows no power blips for 2 months.
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All three PCs had drivers updated in the past month, prior to the problem. I checked with the vendor and they have issued no new updates.
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Motherboard is new and was installed last November. It’s kept in a clean environment.
I’m willing to believe it’s a motherboard problem, that every time I inserted a USB 3.0 drive it somehow caused a fatal hardware problem on that device, yet USB 2.0 devices were unaffected. In order to test that theory, I need a working USB 3.0 drive that I’m willing to sacrifice. Then, if that proves out, I have to make a leap of faith and replace a 6-month old motherboard hoping that the problem disappears. Not to mention replacing the failed drives, unless SanDisk will replace them (something I seriously doubt).
Unless you see any further ways determine the exact cause, I don’t see that I have much of a choice.