if you are using afterburner or wattman, take note that there is a checkbox for applying same voltage to all cards, if you see that - uncheck it - hope that works
You will be surprised but when I've checked it for my 3x R9 390 cards all three started to mine with 3.9MHs
Smth wrong with my Win/Drivers/Hardware
Which I have to figure out how to solve - right now have 12 hours without mining
