All your BIOs option set to GEN 2 or 1?. That seems to be a very specific issue.
I will also suggest checking to make sure the PCIe slots are set to Gen1/2? Although I actually think mine are set to Auto and never had a problem.
How much higher is your total output power since changing to the dagfix version?
i tried this, set PCIe slots to gen 1, all my cards dropped to 5MH/s one to 10MH/s then switched to gen 2, 3 cards got 29MH/s the others 1MH/s and 5 MH/s, tried combinations of GEN1 and GEN2 nothing worked, GEN3 gave me exactly the same results from before, GPU3 with 3 hashes less, still no fix