Today when I tried to boot my X299 Dark nothing would come on and I kept getting EE error code on BIOS LED. On suggestion of EVGA Tech Support (thank you Christian!) I switched from BIOS1 (on board chip) to BIOS3 and after that I was able to boot fine (thank God for practice of keeping fallback BIOSes available).
Then I switched back to BIOS1 and again got EE on boot confirming it is something about that BIOS.
So I used BIOS3 to reflash BIOS1 and after that I was able to boot with BIOS1.
Which makes me ask what in the world could corrupt BIOS on chip that was working just fine for weeks prior to this?!