COM 1 Frequency Swap Error

When I enter a new frequency into a COM1 radio and press the swap button, the frequencies appear to swap OK, but a second later that new frequency which is now the Active is replaced by the Standby Frequency, so both radio windows now show the Standby, and my newly entered frequency has disappeared. The COM2 radio seems to work as it should. I cannot think that this is caused by some menu setting!
I first encountered this with the FENIX A320, but then checked the default B747, and this does the same, so I suppose it is an MSFS error, rather than an individual aircraft problem. I am loathe to start re-installing or repairing the installation without some advice. I have checked to see if any peripheral is programmed to operate COM1 radio, but everything seems OK. I also have FSUIPC7 installed, but no mapping seem to link any control with the COM1 radio!

It could be conflicting with the default ATC window. They kind of sync with one another.

I think you may be correct . I tried turning off AI assisted ATC communication, and it seems to have solved the problem. So far, with the FENX A320, it is now OK. There are so many options available in MSFS, it is difficult to know the best settings!