I actually have a few theories in the case of mine. I don't have a mainstream I class processor to test with however I have other issues with this mobo and I'm hoping the issue is actually a malfunctioning processor in my case.
1) I have a replacement zeon coming in the mail to test it as I'm also currently limited to the first memory channel only. I had all 3 populated originally w the max possible and it only saw the first 8 gigs. I spent over a week scrutinizing all the discrete components on the board looking for any differences in placement etc as some people mod their motherboards, and this was a used board given to me from a fellow tech after my last machine died a year ago.
2) I'm looking at replacing the bios chip if that doesn't work as I'm unsure if it was the original bios from EVGA or something the company that resold it in a "super high end custom build machine" config...I have seen some of the nutty things some of those companies did and the bios I originally saw before I flashed it w the "proper" EVGA one looked hinky... ie multiple functions not showing, custom splash screen etc. Happily I'm quite conversant/handy w a reflow gun or soldering iron... I was one of the high end vape mod builders when nice was penstyle device...lol so replacing a component here or there is no biggie.
Heck the case this mobo is in is custom, made of wood and soon enough going in a slide out access tray in my tinyhome I'm building...I'm building its final power supply to run off the 12vdc lighting battery bank. I went for my own build as I saw no reasonably priced units premade... best I saw was 450 watts and this machines final requirements will be in the 700-800 watt range when running full bore when I use it for gaming. currently it's pulling only 436 but I don't have the watercooling on it yet.