board a -------- has 3 pcie jacks
board b -------- has 3 pcie jacks
board c -------- has 3 pcie jacks
on board a pull the 3 pcie cables run for a day see if you do say 8.5-9 or 4.2 -4.5
repeat the next day with board b
repeat the next day with board c
my guess is one of the 3 boards is sick the 3 day test above should let you which one is sick
good luck