Yeah I thought so to so I spammed uninstall on the audiocontrollers on different ports and then on the one I had problem with and then the whole thing seemed to arrange itself in a way that it didnt cause a conflict. Since you have tried everything else (same as me) im still thinking this is your best bet to mess around there.

Just in case, im dont think it matters, im running 4g decoding enabled, but gen2 pcie link (most recommend gen1). Also,  im sure you have your monitor connected to the correct pcislot (16x) but that is a problem I started with... couldnt get the cards to install the right way for the life of me before I got that out the way 

Anyways I hope you figure it out, I know how frustrating it is.

Try uninstalling hd audio controllers, not just deactivating them

Guys!! I got all six working. What did it was actually the fix in https://forums.geforce.com/default/topic/470858/code-12/ that someone suggested to you Yoledo, I suggest you try it again if you havent done what i shortly describe:

More exactly going to the 'memory' tab,  and inactivating hd audio controllers under pci root port #1 or in your specific case the pci-e port that aint working.

No restart no nothing required, exclamation mark just went away.

Good luck!

Well first of all as I said I had just 4/6 and couldnt do anything. So I cleaned drivers and started by plugging them in one by one, thinking there was a problem with me installing windows with all cards hooked up. Then I got stuck on the third card. 2 working, 1 with code 12. So I did all the fixes, regedit hackflags, updating bios to ver1.30 enabling 4G-decoding option, turned off onbard audio etc. Changed swapfile to 16gb-32gb.

When nothing of that worked I figured after reading this thread and it seems to be an problem with windows 10 ver. 1079, okay I'll plug in all six and just mine with however many cards I can. But then 5 cards run problemfree, and code 12 error on just 1. So thats what I did, cant explain it any better, sorry. Mining at the moment with 5 and only hope of getting 6 working is this thread it seems...

Following this thread since i got the same problem after updating Windows. For while I could only get 4/6 gpus working (code12) on the others but trying all possible fixes got me to 5/6. Now done wasting time finding a solution, 6/6 cards worked before win update....

Hopefully someone solves this, I maxed out my technical potential on this one...