some times even other gpu..i change risers as well..pcie slots as well..with 5 gpu working well one day or sometimes few hours,and just crash to 0 mhs..i was thinking its problem with gpu..but i did some benchmarks..gpu work fine..games as well..really strange..right now rig works with 4 gpu without any problem.
Did you try to plug 4 cards on Silverstone 1000w PSU and 5th card to 850w PSU which is used for motherboard &...?
Just to be sure is your PSU is enough for all 5 cards.
did you test the ram memory?