Funny thing, I had 7600c36 (2×16GiB) stable with your exact same board and a 13900kf, recently updated to a 14900kf and it is Not stable anymore @7600

I’m now running the 14900kf with 6400c32 (2×32GiB)

Pretty stable and cannot tell the difference

So it seems, at least in my case, bad 14900kf IMC

I may return it until January 31st (amazon)