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Guys, did you find where your problem was ?
I'm having a similar situation, everything is almost exactly as Mydi described it, the only difference is that in the last day from time to time I see a message from Claymore miner: "GPU #3 got incorrect share. If you see this warning often, make sure you did not overclock it too much". I'm not sure what is "often" in this case. I see this message once or twice each hour. Until now, for a week or so, my SMA was very stable and very close to the reported hash rate. Now it is down to approximately 2/3 of what it was.
I'm thinking - maybe this particular GPU is not entirely stable at the clock rate I specified. Still, it is a bit strange because the other GPUs (1060) are exactly the same, clocked exactly the same way and the incorrect shares are comming only from this GPU (#3). I'm not sure if this caused the problem because I've seen the same warning in the past, though, probably not so often.
I lowered the clock a little and I hope this will solve the problem...
If you have any similar experience, please share.
P.S. videocard in question is: Zotac 1060 mini (Micron memory), clocks are: +125 +800
Mining ETH only, the Zotac gives me about 24.0-24.3 MH.