Would this be anything to do with the change in the manufacturing process a while back, where these drives are now recognised as ‘fixed disks’
Unlikely. I don’t know how Linux displays drives as Fixed or Removable but try them in a Windows machine, then use Windows Explorer to see if it shows them as Removable or Fixed.
Another possiblity I think would be USB 3.x vs USB 2.x support of your hubs. Contacts are different for the two devices.
