I'm having the same issue - can't get past 16 MH/s with a Red Dragon RX580 8Gb Hynix!
Interestingly enough, I can only get 33 Mh/s with a Vega 56 which seems like 50% less than anyone else.
Are there any other settings which may be bottle necking this ?
This applies to ETC / ETH single and Dual Mining in Claymore, standard drivers, no BIOS mods.
Edit: just found this discussion: https://www.reddit.com/r/EtherMining/comments/6hfivj/hd_7970_hash_rate/