I'm with Greg on this. You must be able to sort this out on a programming track (service mode) whatever your command station.
I see earlier you have read CV50 value 19 which I think is Motorola, AC analog and DC analog "protocols".
Have you tried setting CV50 to 0 (just DCC) or 2 (if you want analog as well as DCC).
If you want a short address change CV29 to 6 (default for 20752) and CV1 to 3 (or whatever short address you want).
If all else fails you could try a decoder reset by writing 8 to CV8 then try writing CV50 to 0 (or 2).
Manual online here: https://cdn.shopify.com/s/files/1/0279/4422/2794/files/instructions-LGB-20752.pdf?2136
Thanks Dave, when I try to debug a problem, I try to go back to the most simple and failsafe procedure.
Bringing POM (Programming On the Main) into the equation just adds more possibilities for something wrong.
In the beginning of this thread, alarms went off when there was inconsistent reading of CVs, thus we really had no idea what was going on, the issue being with the system, the decoder, or possibly the decoder installation.
Let's get the most basic programming functions working reliably.