OK, very good. Now we now the PF3 part of writing the frequencies is working.Sorry I got there in the end, below is data in that file, Correct for my flight.
Timestamp=201903071326
(and you have another workaround to get the frequencies: use the contents of this file)
Next step: If PF3_Display shows other data, it has to read it from somewhere. Is there (or has there been) a second installation of FSX or P3D on this computer in a different directory?