After a lot of uninstalling/reinstalling of drivers and software, my problem is solved but I’m not entirely sure why. Nothing individually made any difference. It’s as though there was some sort of cumulative effect.

One notable change is that the notorious “Device . . . could not be migrated” message has disappeared. I was getting this on virtually all USB devices, most (but not all) of which continued to work regardless. It may just be coincidence but it was around the same time as uninstalling all the ‘history’ of USB/Disks/Portable devices/and others from within Device Manager (by clicking View/Show hidden devices then rightclick/Uninstall all the ghostly greyed out items).

Now instead of Events showing:
Device deleted, Device not migrated, Device configured, Device started

I just have:
Device deleted, Device configured, Device started

However I’m sure I went round the loop of doing the Uninstalling from within Device Manager more than once before achieving this so it could be coincidence.

Anyway, the Satmap works (for now) in both USB2.0 ports and USB3.0 ports, so maybe my USB2.0 controller theory was completely irrelevant. Apologies for any red herrings.

Many thanks to all of you who took the trouble to reply.