I got a problem here.
6 cards in a rig. R9 390. 1100/1500 +50 power lim.
Win 8.1
Driver 15.12
12 gb memory
H81 pro btc + g1840
The problem is miner hangs when 1 card goes to 0 speed. Can't even close the window with miner. Only reboot helps.
The card that hangs likely has a USB-riser thats on it's way out. Try changing just that cards riser.