I have an interesting one here.

My 7GPU RX570 rig with flashed bios has 30.6MH per card with Claymore 11 under WIN10

Running the same rig under Ubuntu the miner at start reports similar hashrate to WIN10:

• ETH: GPU0 30.570 Mh/s, GPU1 30.629 Mh/s, GPU2 30.615 Mh/s, GPU3 30.611 Mh/s, GPU4 30.618 Mh/s, GPU5 30.631 Mh/s, GPU6 30.632 Mh/s

But then it goes lower and stays this way:

• ETH: GPU0 30.112 Mh/s, GPU1 30.160 Mh/s, GPU2 30.165 Mh/s, GPU3 30.158 Mh/s, GPU4 21.060 Mh/s, GPU5 21.071 Mh/s, GPU6 30.188 Mh/s
• ETH: GPU0 30.119 Mh/s, GPU1 30.165 Mh/s, GPU2 30.159 Mh/s, GPU3 30.159 Mh/s, GPU4 30.150 Mh/s, GPU5 30.177 Mh/s, GPU6 30.160 Mh/s

Any idea why ?