Comment 2 for bug 1815588

Thanks for upgrading to 18.04 now I can use my system as is for the same tests.

At least the warning is about a USB 3 device being attached to a slower (virtual) USB hub.
The default virt-manager/libvirt usb controller is piix3-uhci which is USB 2.0
The controller type can be changed thou, but one step at a time

I fetched my USB 3.0 thumbdrive and will do the same pass-through you are struggling with.

With the default uhci controller in the host and passing through the USB 3 drive it works immediately (it is attached). But I get some complains later on about usb resets.
  usb 2-1: reset SuperSpeed Gen 1 USB device number 3 using xhci_hcd

The guest shows "normal" "usb 1-1: New USB device found" ...
And finds the device.

Next I tried a USB 2.0 thumbdrive.
That works as well - even without the bus reset warnings.

Lets switch the USB controller type if it gets even better for the USB 3.0 thumbdrive.
(Needs shutdown/start of the guest after changing to USB 3 in the virt-manager UI)
BTW what virt-manager calls "USB 3" is in libvirt really "nec-xhci" and I see a USB 3.0 root hub in my guest.

Note - I found that the reset message on the host seem to be normal and ok, it targets all "siblings" on the same bus tier as the device that was just removed from the host.

Attaching USB 2 device - works and appears in the guest
Attaching USB 3 device - works and is "slotted" into the USB 3.0 port