It's not that the IMC can't run or boot the RAM. After all, there are inummerable people running Micron E-die with 5900X. How could that be if the 5900X IMC is the issue. Unless, of course, the chip passed QC but for some reason now fails for some freakish reason... but I first have to presume that the issue is not intrinsic to the 5900X, but rather a function of your total system.
The motherboard and BIOS are compatible with your 5900X, but the motherboard is not (technically) compatible with your RAM. So if the 5900X looks intact, my suspicion is that the IMC and 5900X are probably fine (after all, it passed QC and worked coming out of the factory), and it's just the unfortunate case that 5900X + your mobos + non-QVL RAM doesn't work, even if you got lucky and the 3700X + your mobos + non-QVL RAM does work.
I'd call Microcenter - mine has let me bring in "within 30 day" parts in order to help solve problems and prevent a return. They may be willing to let you try some QVL-compatible RAM sticks, or at least some different RAM sticks, to see if that solves the issue. Hopefully it does!