Disappearing MemTest86 errors after BIOS reset at identical RAM Settings

At the time of buying my RAM, I did not know that AM5 does not like 4 DIMMs. I only educated myself on what the best MT/s Speed is and went for such kits. This is why I have 4x8GB DDR5-6000 CL36-38-38 with my Asrock B650M Wifi Pro RS and an R7 7700.

I’ve always had some weird behavior, which I brushed off as something that comes with linux. Most prevalent was: After boot up, having typed in the password and pressing enter to log in, it takes just a couple seconds too long to get into the desktop. This is followed by an insanely laggy mouse, if any mouse movement is possible at all. Most of the time, its not even possible to shut down the pc using KDEs UI + the keyboard because everything is so laggy.

Keep in mind that this only happend once a week and was fixed by a reboot. But there are other things which might be a symptom as well.

Recently, I’ve seen the advice against 4 DIMMs in L1T’s videos and decided to invest my free time today into checking my ram. I threw MemTest86 on an usb stick and ran the tests. 2000+ errors in the first 5 tests and then it froze. This was at 5600 MT/s, I didnt note down the timings. They might have been the AGESA default, but I might have tuned them.

I’ve clocked down my RAM in 400MT steps and kept encountering errors until my system wouldn’t even reach BIOS after applying the a step down. This might have been because I left “Context Restore” on while stepping down. Because of this the mainboards chip probably confused itself with the old context.
I’ve reset my BIOS, everything booted again and I started from the bottom up. 3600 MT up until the AGESA profile with 5600 MTs and 36-38-38-80. Everything is running fine now.

How can that be? Why would a BIOS reset fix the RAM problems? The MT/s are the same, and the timings are probably the same.

Below is the output of the latest MemTest86 run. The latency and throughput numbers cannot be trusted, these change with every boot into memtest without changing any RAM timings etc. Testing the actual throughput using the “RAM Benchmark” tab, I consistently get ~40GB/s, but this doesn’t test latency. Across the many reboots while bumping up the memory speed in smaller steps, the latency was always reported between 54-94ns