Hi ZH - as skypilotYTS suggested, I have deleted and reinstalled the drivers, and this seems to work most of the time, but I still have to unplug the USBs and then plug them back in again sometimes.
This however is not too much of a burden - at least both the radio panels now work together OK (they didn’t when I first connected them up shortly after MSFS was released).
Regards, Alasdair (aka Flybasher…)