@Mastakilla, exactly what server grade x470 asrock rack mobo did you mention in your first message in this thread?
I have been trying now with an ASrock Rack X470D4U (latest bios with ECC enabled, ECC injection enabled, Platform First error handling disabled) with a Ryzen 9 3950x with no luck.
I am using Passmark Memtest pro 8.4 rc2 Build 1001 but Passmark is still troubleshooting on the basis of my debug logs.
AMD is assuring me that a previous setup I tried
Asrock x570 (AMD AM4 socket, AMD X570 Chipset ) Creator with a Ryzen 9 3950x
does support ECC correction and reporting but I started using memtest86 pro after I had returned that setup.
I am willing to try that setup again in case the audience here will find that useful.
Anyway could it be the problem is not the CPU or Bios persee but perhaps other components?
I have for one on my X470D4U mobo the following:
Processor System
CPU - AMD AM4 Socket Ryzen™ PRO/ Ryzen™ 2nd and 3rd generation series processors
Socket - AM4 PGA 1331
Chipset - AMD Promontory X470