re-check all your PSU cables...every time I have a card that won't work it's related to the cables and connectors
PSU cables are plugged in, again, i tested individualy each card and each of the 6 cards works fine. so that's not the issue.
Try looking for a "Enable above 4G decoding" or a similar option in the BIOS. If you can't enable it/can't find it/still does not work it is probably Windows 10 issue (if you are using it) or driver issues.
Yeah i forgot to mention, Windows 10 ^^I didn't find enable 4G in bios, all i found was Gen 1 or Gen 2 in some options but i don't know what it means.
You might want to turn the PCIe slots to Gen 1 and test the risers individually. If all of them work then I think it's a software issue.
all risers are working fine since i tested every one when i plugged each card separately from the rest.
In my opinion, it's not an hardware problem, more a software one
i'm gonna try some drivers that citronik gave me on another topic, will see if it works.