While having the same issue with Micron/SK Hynix & Samsung I figured it's not about 2133, 2400 and/or 2666Mhz or the vendor. My SM boards just do not like 4DRx4 ram. Every 2Rx4 ram, no matter of the vendor and/or frequency just works fine. So don't let someone mislead you that EPYC's do not work with 2133Mhz. They work perfectly fine. My H11SSL-i and H12SSL-i just don't like 4DRx4 while my Gigabyte MZ32-AR0 just doesn't care as long as I use max 8 sticks only. So it has something to do with the 4DRx4 typology.