4 Dimms are often a lot harder to drive at higher speeds on AMD (not sure about intel as the most recent stuff I’ve dealt with was 8th/9th gen.
Ive had issues hitting 3600 on a 5800x3d and 4 dimms while a 5900 was driving them at 3866 no problem. However, 2 dimms ran fine at 3600mhz on the 5800x3d
I went through a lot of issues with a 4 DIMM setup with my 5950X, ultimately I got it to work at 3200MHz but in the future I am just gonna stop worrying about e.g. 3200MHz and just fallback to JEDEC speeds at first sign of trouble. I’m not really convinced that the memory speeds are that important
Old topic…but here goes…
When upgrading from 2 sticks to 4, you need to install the matched pairs into the same bank. With 2 sticks you install them in A2-B2. When you go to 4 sticks, take one of the original ones out and put those in A1-A2 or B1-B2. Then use the free bank, A or B, for the new matched pair.
Ryzen is trying to organize the banks in ranks before it combines the channels for dual channel. The other way means you ALWAYS have unmatched ranks in the same bank.
On my system, it would do XMP just fine with 4 sticks, but there was something off, random instabilities. Since rearranging the pairs into banks, the CPU runs cooler and subsequently faster. Not to mention, my 3600 RAM works at 3800 now, and can get up over 4000, using G.Skill 3600 16-19-19-39 RAM
Try to rearrange your modules and see what happens
Typing this on an 5800X3D with 4 sticks of Kingston DDR4-3200 ECC RAM.
I have another 5950X, originally a 5800X, using the same Kingston brand/type sticks from three different purchases (2+1+1), because at the time DDR4-3200 ECC was rare and expensive.
As far as I can tell from their parts numbers they are sometimes even mixed manufacturers, but they all work just fine with ECC support and nominal speeds. That’s where the Kingston brand pays for its premium on ECC.
Both boards refused to work with DDR4-2133 and DDR4-2400 ECC DIMMs I hijacked from existing machines when they newly arrived.
BTW: interesing rumor on the V-Cache not having ECC. Since the base tech is originally EPYC and the CCDs aren’t desktop specific until they are packaged, I find that very hard to believe.