Ubuntu won't boot with more than 4 GPU's

[flux]

hanging while loading X means the driver is stuck in iowait trying to communicate with a gpu that was there, but is now not there. the issue is most likely with your risers. if it's not the riser, then you may have a bad gpu or two.

Thanks for the info. What if the risers have been rotated as well though? I've tried for example booting with first 4 then adding the 5th or booting with last 4 and adding the 2nd card and I still have the same issue.

Could the risers just be creating an issue when that many are being used? Because it doesn't seem that any one of them is particularly bad. I will retest though.