USB3 loopback enumerates but is not acknowledged

[NeilVP]

Why might a USB 3.0 loopback tester enumerate on a USB hub, show itself as being connected to a USB3 port but not be seen by the attached PC?
A mouse can connected through the same port on the same hub to the same PC and work. The Loopback tester is acknowledged when connected directly to the PC (and seen in Device Manager) but not if it is connected through the hub. It sounds like an issue with the hub to me but can anyone suggest what it might be? (Windows 10 & 11 pro)

[David (PassMark)]

There is a table here showing how the messages in the LCD screen of the loopback plug correspond to state of the device.
https://www.passmark.com/support/usb...rity_audit.php

If the plug looks like this

Then the most common cause is that there was no available device driver installed for the plug. Is this what the screen looks like?

On a few hubs we have also seen problems when USB2 and USB3 devices were on the same hub. So as a test remove any other devices on the hub.