First question - what PSU do You use? Can You change PSU for testing? I dont have much rigs - around 25 - and I have seen that most problems start with bad or noname PSUs.. Now I am using just Corsair, Seasonic, Antec or bequiet! PSUs. And problems went away..

Other hardware is standard ( BTC Pro mobos, G1840 processor, 8GB ram, corsair SSD ).
Hi. I'm use brand new AeroCool Higs 850. Yes, I changed to another PSU. But this does not solve the problem.
Now tried the V8. Claymore great work! Thanks.
For the same hashrate for all GPU. I needed to restart miner 6 times! Six times!

ZEC: 11/24/16-21:41:28 - New job from eu1-zcash.flypool.org:3333
ZEC - Total Speed: 585.107 H/s, Total Shares: 487, Rejected: 1, Time: 00:15
ZEC: GPU0 197.356 H/s, GPU1 192.574 H/s, GPU2 195.177 H/s
DevFee: ZEC: 11/24/16-21:41:28 - New job from eu1-zcash.flypool.org:3333
DevFee: ZEC: 11/24/16-21:41:29 - SHARE FOUND - (GPU 1)