I posted here almost exactly 24hrs ago whining about my M.2_1 not working. Well guess what - after testing each card individually I found the culprit. The issue was yet again a f*cking bad Chinese riser part. Yes, the M.2 cards were 100% fine BUT this time I found a dead Mintcell Ver. 8 riser kit bad. It was the small piece that plugs into the PCI-E and turns it into USB on the motherboard side. I have found three bad pieces like that now! (two Mintcell ver. 7 and now now Mintcell ver. 
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My hypothesis that all of these "I can only get four cards work" or "I can't get the M.2 risers to work" blah blah blah are all attributed to rubbish chinese riser parts. I can't even imagine how much time has been wasted because those as*holes couldn't do any QC on their junk. It was very suspicious in my mind that so many people have 8+ cards on their Z270-P's yet a select few of us can't get anything to work.
Well there you have it - VERIFY 100% THAT YOUR RISER KITS ARE COMPLETELY OPERATIONAL INCLUDING THE USB CABLE, THE PCI-E TO USB ADAPTER, AND THE PCIE BOARD ARE GOOD.
. My hypothesis that all of these "I can only get four cards work" or "I can't get the M.2 risers to work" blah blah blah are all attributed to rubbish chinese riser parts. I can't even imagine how much time has been wasted because those as*holes couldn't do any QC on their junk. It was very suspicious in my mind that so many people have 8+ cards on their Z270-P's yet a select few of us can't get anything to work.
Well there you have it - VERIFY 100% THAT YOUR RISER KITS ARE COMPLETELY OPERATIONAL INCLUDING THE USB CABLE, THE PCI-E TO USB ADAPTER, AND THE PCIE BOARD ARE GOOD.