More than 3 cards, less hashrate

[ThatPR]

I am testing your miner and I have a small problem. If I have connected 3 GPUs, all have around 30,15Mh/s. But If i connect more then 3, one of them has smaller hashrate about 28 Mh/s.
All my GPU are gigabyte rx570 4GB with modded bios.
I tried 4, 5, 6 GPUs and everytime, only one has smaller hashrate. I tried to change GPUs but the same problem on the last device number.
OS: Windows 10 FCU

Thank you for your help

[ethash]

I tested the issue but I haven't seen lower hashrate . Can you check your bios settings?

[ThatPR]

I have Gigabyte GA-H110-D3A. I set minning mode on, integrated graphics on, power on AC on. Nothing more, what should have an influence on mining. But I found out, that exactly same problem I have with claymore v10.0 too (you use the same kernel I think?). One GPU has everytime lower hashrate. It dont care, that I change GPUs PCIe slots, everytime device number 3 is worse, then others.
And another problem, which I found out with your miner. After 2 days of mining, my total hashrate goes down about 10Mh/s and in ethermine.org dashboard i see about 30Mh/s current hashrate lower.