Well, I've got the USB stick on the scanner back - sort of.
It seems there's a network discovery issue with Windows 10, which I'm a bit surprised about as that's something I'd think businesses would use a fair bit. After poking around for a while it seems that although I can see the printer and can access it, it's not being found automatically by Windows 10. The same goes for the WD MyCloud backup box. I can map drive letters to them, create shortcuts to them, all that stuff. Windows 10 won't automatically discover them though. The only thing it will automatically discover is your laptop - when it's turned on.
To get around this lack of automatic discovery I used Explorer and "Add a network location" to add the USB drive to my list of network locations and mapped drives.
Not a complete fix, but at least I can now access the USB stick on the scanner.
What's even better is that the networkj location persists across a re-boot.