I've encountered this strange issue in the past few months where my hashrates mining ethereum will intermittently drop from about 30 Mh/s to 20 Mh/s. Everything was stable at around 30 Mh/s before this and I don't know what has changed to have caused this. When I look at my GPU usage in MSI Afterburner, I can see that there are frequent dips instead of a constant 100% usage.  Is this a power supply issue? I'm using a Seasonic 1250W Gold power supply and that's powering 6 GTX 1070's and 2 GTX 1060's.  I set the Power Limit to 60% in Afterburner for all 8 cards and my smart plug is measuring about 900W of consumption.  I'm using overlock settings of -100 on the core clock and +650 on the memory clock in Afterburner, but I've since reset both overclock settings to 0 just to see if that would solve the issue - it does not.

I'm using Windows 10 and Claymore.  I've never seen this issue until about a few months ago and I wonder if the Byzantium update affected things?  The other weird thing is that if I switch my rig to mining Zcash, I don't have this problem at all and the GPU usage when mining Zcash is at a constant 100%.  So the issue only seems to happen with ethereum.  I have a second PC that only has two 1070's, and this issue does not surface so I'm really puzzled. That's why I'm thinking maybe it's the power supply?

Can anyone help?