I have a system of 2 1070s, one Gigabyte Windforce, the other Asus Aorus.
The problem is, dstm miner crashes when I use both cards. So, at certain settings (stock and OC)
I can mine with a single GPU for infinity, but when I use both - I experience several
"light crashes" which are cured by resetting the driver and restarting the miner - and then a complete system freeze.
Even running both GPUs at stock.
Sometimes it can take a day, sometimes an hour to do so.
I can say that the time required for a complete fail has decreased, it took more time earlier.
I use Win7, a 700 W PSU, MSI AB for overclocking. One GPU is in the 16x slot, the other is connected via a raiser.
The motherboard is a bit old (from 2012), if that's important. And a double core proc (core2duo) and 2 Gb RAM.
Driver version - 390.77
I've similar problem when i tried same config one card directly in 16x slot and second in raiser. In my case second card didn't work at all. As soon as I put both cards in raisers it has started to work without problems.
I think when you connect one card directly to x16 slot on older mobos it use all PCIe lines and then other cards will not work properly.