I've built 2 7 GPU mining rigs. Setup is the same for both of them.

Setup:
7 x Asus ROG Strix Radeon RX 580 8GB GPUs
1 x Z170A Gaming M5 Motherboard
1 x Inte Pentium Processor G4500 3.0 GHz CPU
1 x SanDisk SSD PLUS 120GB
2 x EVGA SuperNOVA 750 P2 PSUs
1 x Corsair Vengeance LPX 4GB DDR4 3000mhz
1 x Add2Psu PCU Adapter
7 x 16x to 1x Powered Riser Adapter Cards

OS: Xubuntu 16.04
Driver: AMDGPU-Pro Driver Version 17.10 for Ubuntu 16.04.2
Mining Software: Claymore Miner 9.5
Pool: ethermine.org

Claymore settings:

export GPU_MAX_ALLOC_PERCENT=100

./ethdcrminer64 -epool us1.ethermine.org:4444 -ewal MY_MINER.Miner02 -epsw x -etha 0 -mode 1 -tt 68 -ttli 79 -tstop 85 -allpools 1

GPUs are stock and not overclocked.

The problem is I'm getting very low hashrate on 2 of my GPUs. Maximum hashrate I've seen was only 141 Mh/s

Example logs:
ETH - Total Speed: 141.077 Mh/s, Total Shares: 5887, Rejected: 1, Time: 63:14
ETH: GPU0 4.140 Mh/s, GPU1 16.052 Mh/s, GPU2 24.174 Mh/s, GPU3 24.186 Mh/s, GPU4 24.185 Mh/s, GPU5 24.173 Mh/s, GPU6 24.168 Mh/s
--
ETH - Total Speed: 141.075 Mh/s, Total Shares: 5888, Rejected: 1, Time: 63:14
ETH: GPU0 4.140 Mh/s, GPU1 16.054 Mh/s, GPU2 24.178 Mh/s, GPU3 24.166 Mh/s, GPU4 24.182 Mh/s, GPU5 24.182 Mh/s, GPU6 24.173 Mh/s
--
ETH - Total Speed: 141.080 Mh/s, Total Shares: 5889, Rejected: 1, Time: 63:15
ETH: GPU0 4.140 Mh/s, GPU1 16.052 Mh/s, GPU2 24.173 Mh/s, GPU3 24.183 Mh/s, GPU4 24.175 Mh/s, GPU5 24.183 Mh/s, GPU6 24.175 Mh/s
--
ETH - Total Speed: 141.145 Mh/s, Total Shares: 5889, Rejected: 1, Time: 63:15
ETH: GPU0 4.140 Mh/s, GPU1 16.053 Mh/s, GPU2 24.198 Mh/s, GPU3 24.202 Mh/s, GPU4 24.183 Mh/s, GPU5 24.200 Mh/s, GPU6 24.169 Mh/s
--
ETH - Total Speed: 141.048 Mh/s, Total Shares: 5889, Rejected: 1, Time: 63:15
ETH: GPU0 4.140 Mh/s, GPU1 16.053 Mh/s, GPU2 24.177 Mh/s, GPU3 24.184 Mh/s, GPU4 24.170 Mh/s, GPU5 24.187 Mh/s, GPU6 24.137 Mh/s
--
ETH - Total Speed: 141.182 Mh/s, Total Shares: 5890, Rejected: 1, Time: 63:15
ETH: GPU0 4.141 Mh/s, GPU1 16.053 Mh/s, GPU2 24.195 Mh/s, GPU3 24.173 Mh/s, GPU4 24.189 Mh/s, GPU5 24.217 Mh/s, GPU6 24.215 Mh/s
--
ETH - Total Speed: 141.061 Mh/s, Total Shares: 5890, Rejected: 1, Time: 63:15
ETH: GPU0 4.140 Mh/s, GPU1 16.052 Mh/s, GPU2 24.179 Mh/s, GPU3 24.179 Mh/s, GPU4 24.161 Mh/s, GPU5 24.174 Mh/s, GPU6 24.176 Mh/s
--
ETH - Total Speed: 141.054 Mh/s, Total Shares: 5890, Rejected: 1, Time: 63:16
ETH: GPU0 4.140 Mh/s, GPU1 16.054 Mh/s, GPU2 24.172 Mh/s, GPU3 24.169 Mh/s, GPU4 24.176 Mh/s, GPU5 24.172 Mh/s, GPU6 24.172 Mh/s
--
ETH - Total Speed: 141.077 Mh/s, Total Shares: 5891, Rejected: 1, Time: 63:16
ETH: GPU0 4.139 Mh/s, GPU1 16.055 Mh/s, GPU2 24.171 Mh/s, GPU3 24.176 Mh/s, GPU4 24.172 Mh/s, GPU5 24.182 Mh/s, GPU6 24.181 Mh/s
--
ETH - Total Speed: 141.155 Mh/s, Total Shares: 5891, Rejected: 1, Time: 63:16
ETH: GPU0 4.140 Mh/s, GPU1 16.065 Mh/s, GPU2 24.170 Mh/s, GPU3 24.208 Mh/s, GPU4 24.213 Mh/s, GPU5 24.177 Mh/s, GPU6 24.182 Mh/s

Sometimes I'm even getting low hashrate on almost all GPUs:

ETH - Total Speed: 49.076 Mh/s, Total Shares: 5880, Rejected: 1, Time: 63:07
ETH: GPU0 4.140 Mh/s, GPU1 16.060 Mh/s, GPU2 5.616 Mh/s, GPU3 5.617 Mh/s, GPU4 2.945 Mh/s, GPU5 5.501 Mh/s, GPU6 9.197 Mh/s
--
ETH - Total Speed: 71.613 Mh/s, Total Shares: 5880, Rejected: 1, Time: 63:08
ETH: GPU0 3.015 Mh/s, GPU1 5.215 Mh/s, GPU2 5.273 Mh/s, GPU3 4.927 Mh/s, GPU4 4.747 Mh/s, GPU5 24.216 Mh/s, GPU6 24.220 Mh/s

What could be a problem here? I see mostly people using Windows for Ethereum 7 GPU mining, could it be OS problem? I prefer Linux for easier remote command line management and also I know it better than Windows.

I have the same issue on both on my rigs.

Thanks a lot ahead for any help.