Every GPU testing one by one are working?
-What drivers are you using?
-PCI Gen1 to all 3 points?
-Power supply?
I had the version H270 from asus and no problem with 5 or 6 cards.
-Tested individually, they all work
-Risers/cables tested
I had all 3 options set to GEN1, switched them to GEN2, switched them back to GEN1 and now it's working with 6 gpus....
Wow... What an annoying problem