Just to update on my thread, I reinstalled Windows last night on the new WDBlue drive, got that fully updated. Installed GeForce experience and updated the 2070S drivers.
This morning I installed the Oculus software and reconnected the device and...
...
...
IT WORKED!
Therefore, I don't need to send it back to Oculus, kids are conducting further testing as I type.
However, what the hell happened to make it go wonky that was clearly software related so that only the nuclear option of a new drive/Windows reinstall fixed it?
An important difference is now in the Oculus software under Settings>Beta>Restart Oculus software - this option now works.
Will have to slowly install other stuff and see what happens.
Really have appreciated the advice in this thread, thanks