I have copied the BIOS off of my X470 and X570 and looked the code based closely.
What I have concluded is that the AMD AGESA code based needs to be revamped significantly. It is now clear why the platform is so sensitive to RAM. A redesign of the memory controller logic is needed.
I have also concluded that the X470 Gaming Plus is a cheaper 4 layer board with the top chipset used. I would have expected a slightly better platform but in the price sensitive world cost matters to many.
My X570 is more expensive and the use of PCIe 4.0 probably motivated the 6 layer approach.
So I stand by my assessment that the memory logic needs to be revamped as well as the device manager.