Strangely this seems to have been fixed for now! I used my computer for a number of hours yesterday and this afternoon whilst having my USB thumb drive attached and I was able to copy and move files across without issue. No random disconnects at all.
If it's fixed I'm a happy bunny but it would have been nice if MS had made this fix public so we knew what had been causing it.
Of well, hopefully this will be the end of the matter 🤞