[_cenw]

The Zen 4 memory controller only sometimes is binned high enough to be stable at 6400. It's likely that linux just loads the memory better out of the box. I had to dial back my 7800 X3D to 6000 after rare but consistent crashes.

You can try OCCT to check if your memory overclock (even with Expo and especially with XMP, those are overclocks) is stable.

You probably have Hynix memory (check your 4 main timings and XMP/EXPO advertised speed) - if you do, these are very save timings you can do that'd probably make up for going down to 6000: https://www.youtube.com/watch?v=dlYxmRcdLVw

[bloopernova]

Thank you, I will check the link out and you've given me some good research to chase.