HI zawawa.

Also experiencing the low hashrate on one card with Neoscrypt
see include screen grab of HWinfo and GG.
cards used are rx470s,rx570s and rx580s with amd blockchain driver.   
from HWINFO seems to be a gpu memory issue.
Otherwise speeds are awesome between 700hs-800khs for my cards
https://imgur.com/DJrNr9q