Hi, I have quite similar problems like in the closed thread “H12SSL-I boots with (8x16gb) memory but wont boot with (8x64gb)”
The motherboard is a Supermicro H12SSL-NT with an AMD EPYC 7502P and 8x HMAA8GL7MMR4N-UH. The LRDIMMs work fine on sockets A, E, F, G and H. With an EPYC 7502P socket C works but sockets B and D don’t. With an EPYC 7282 socket B works but sockets C and D don’t work. Changing the LRDIMM modules around does not change anything. A Huananzhi H12D-8D motherboard shows a similar behaviour. The CPUs were mounted with a digital torque wrench at 1.6 Nm. The Arctic Freezer 4U (Ampere) was mounted with the digital torque wrench at 0.9 Nm. I also cleaned the CPU and LRDIMM contacts with spirit and a brush.
I don’t think the motherboard or mounting really has anything to do with it. From what I understand the first two generations of EPYC CPU’s (7xx1, Naples and 7xx2, Rome) were very very picky when it comes to RAM, and it is not uncommon at all to have RAM issues when pairing them with random RAM.
Starting with Milan (7xx3) CPU’s that reportedly improved significantly, presumably due to an improved memory controller on the CPU package.
This is why I specifically tried to find Milan+ EPYC CPU’s when I upgraded my server a few years ago. I didn’t want to deal with finicky RAM. As a result I have not had any problems in my H12SSL-NT with my Milan CPU (7543)
Since you are having the same issues on both motherboards, I am assuming this is the cause of your problem, and not any damaged or bent pins in the CPU socket, but if you do decide to spend money to fix this issue, it probably wouldn’t hurt to (very carefully) inspect the socket pins under lighted magnification first.
As for what to do about it, I don’t know what to recommend. You could probably try to find RAM that is specifically know to be good with Naples or ROME CPU’s, or try using a Milan CPU.
Based on how difficult it is to get RAM at a reasonable price these days, I’m guessing a CPU is probably the more affordable path (but I have not looked at the numbers, so don’t take my word for it)
If you do decide to go the CPU route, Milan does share the same socket and will work in the H12SSL-NT but it is the last generation that does. Newer Genoa/Bergamo/Siena CPU’s require a new motherboard.
Also keep in mind that EPYC CPU’s can be vendor locked, so make sure that you get a CPU that is unlocked, or it will refuse to boot.
