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