I had same issue with same mobo but 4 dimms total of 32gb.
Obviously all my ram were OK.
I tired everything (changing bios setting, updating bios). But I could never get the bios working with 4 *8gb ram !!
Well what I finally did is remove the cpu fan. Open remove the cpu. And I find a very small dust stuck in the socket. I just give a big blow in the socket. Then put back the cpu. Then close the cpu. Put the cpu fan back.
And surprise I can now use my computer with 4*8gb ram !