Addendum: just tested my USB 2.0 scanner on a different system, but exact same Linux distro and kernel. It has a USB 3.0 chip from Etron
(Etron Technology, Inc. EJ188/EJ198 USB 3.0 Host Controller).
Even with the xhci_hcd driver, the scanner works flawlessly in that system.
That turns the focus on the USB 3.0 controller in the NUC, where the scanner just hangs:
"Atom Processor Z36xxx/Z37xxx Series USB xHCI".
If there will be no pricipal fix in BIOS or in the xhci driver, then please add the BIOS option I indicated !
Thanks for joining the NUC community.
Your feedback is important to us and I thank you for taking the time to communicate this issue. \
I can confirm that one of the last BIOS updates (likely 0040) has solved the problem with the scanner.
So from my point of view a disable switch for USB 3.0 is no longer required.