I have Miner with 6 RX480 cards.
What I have as issue is that randomly my system freezes and therefor miner is stopping to work. I really can't understand why. Cards temperature is constantly 55ish C. Physically everything seems to be okey. I've already checked slots, cables and etc.
I had the same issue when I was mining etheriums. It seemed to stop when we had first version of Zec Claymore Miner. Back then 3-4 days mining without any freezes, but after that basically with every new version my system had the issue. I'm not sure if this was coincidence tho.
EDITED* One thing I remembered when I was mining etheriums one of the workers were stopping and after a minute of mining the system were freezing or miner(claymore software) was stopping to work.
Anyone who has the same issue or if you need more information pls feel free to ask me and I will try to provide it to you.