Comment 7 for bug 1815588

Thanks for your feedback Eero,
I have tested USB 2/3 drives on USB 2/3 hubs now - it is not that in in general a combo of these would fail.

Lets continue to brainstorm what could be the issue ...
I hear from you that your Failing Device is the "Porsche Design Desktop Drive" and that you say is USB 2.0 in comment #6.
But your error thinks it is USB 3.0, maybe there is an issue around that being correctly detected?:
  Warning: speed mismatch trying to attach usb device "Porsche Desktop" (super speed) to bus "usb.0", port "1" (full+high speed)

Super Speed = USB 3

What does "sudo lsusb -v -d 059f:106e" on the host show?
Does the host detect it as USB 2 or 3?

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Further we might want/need to focus on the actual error being "failed to open host usb device 2:2", but you said there are no apparmor Denies anymore. So why is it failing then?
Not recommended in general, but for a try you might set the user your guests are executed at to root to check if this might be a "normal" ownership/permission issue of some of your device nodes vs the libvirt-qemu user that you have. See configs user/group in /etc/libvirt/qemu.conf
I'd never keep it that way, but it is sometimes the easiest way to check for permission issues.

Furthermore you might check the group memberships of libvirt-qemu:
 $ id libvirt-qemu

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Finally I really want to know which access exactly is failing.
After the guest is up (without the USB device yet).
Set up an strace to the open calls like:
  $ sudo strace -e 'trace=/.*open.*' -p <PID-of-qmeu>
Then in the UI hit the "attach USB" and report what was traced

And just to be sure - check dmesg once more if there really is not Denial.