Yeah I'm not expecting them to run x16/x8. What I'm saying is no matter what I do, the MB only detects one at a time, although which one varies, and always at x8 speed, even if it's the top one and it only detects that one.One of the downfalls of sli, they always run at x8/x8 so the board is seeing 2 cards populated if nothing else is.
I thought about it but I was dreading it as getting to them is a pain, but I'll try later and update this answer with the results.Have you tried removing one of the m2 drives to see if that makes any difference. Only so many lanes on z370 and with 2 x m2 and 2 x gfx it may not like it.
You would expect it to default to a lower speed to compensate but worth ruling out