Fresh build, current 3401BIOS, all drivers installed, Win10 Pro, no exclamation points in Device manager, USB 3.1 enabled in BIOS.
I plug a USB 3 memory stick (that works fine in a blue USB 3.0 connector) into the red USB 3.1 connector, and Win10 says a device has been inserted, but it doesn't show up ANYWHERE, not in Disk Manager (so I can assign it a drive letter), not in Explorer, nowhere. Same stick plugged into a blue USB 3 port shows up everywhere.
The BIOS sees it in the BOOT menu, displays its model and capacity, but once Win10 boots it's there, but it's not.
Tried turning on and off the 'USB 3.1 Charging' feature, no difference.
According to many web articles, a USB 3.1 connection should be backward compatible with USB 3 and USB 2 devices, and after finding the onboard 3.1 connector wouldn't properly recognize the memory stick, I installed a ThunderboltEX3 card and drivers, and its USB 3.1 port sees the same memory stick just fine.
Anyone have any idea what is happening here? Anything else for me to try? Is the motherboard just defective?