Sorry for not elaborating further, I was on mobile at the time.
Some hardware implementations of USB3 seem to drop connection. There is no benefit for USB3 speed in the case of Unraid Flash. The archives of the OS are unpacked fresh from flash at each boot into RAM, and the OS runs completely in RAM. Think of it as firmware except easier to work with. Flash also stores settings you make in webUI so they can be reapplied at boot.