I still don't know how you were able to get that low. I'm always around 10 incorrect per 1000 no matter how much I underclocked. Tried different ram timings, drivers, voltages etc. Moot point now that keccak is dead.
That sounds like bad Bios timings. It could also be your -dcri setting. I used 6 or 7 for my RX 580's and 5 for RX 570's. But yes, dual mining profitably is dead for most, at least for now.