both of you have risers on the dead cards am I correct?
I have 20 cards all good all have no risers.
My guess is it is a riser issue.
So funny Phil, this attack against risers

. Though I'll listen to you for my next rig, by not using any riser and placing all the cards on a motherboard, for now all my cards except two cards are connected throught risers and I never had any problem.