Thanks for the reply Chris.
I had scanned and updated previously but since the Bluetooth device was not showing in Windows, I didn't see the Bluetooth driver listed.
Windows 10 had all updates too.
However, I had to physically move my PC and disconnect the power entirely.
After re-connecting etc, Bluetooth re-appeared.
I'm not aware that any Windows/Intel updates occurred in between
I had of course restarted Windows more than once whilst testing but not fully disconnected the power.
Whether it was that, the physically moving or the wind direction changing, I've no idea but back to normal for now.