Are you using Claymore's Dual miner? What is your intensity set at for Sia? I had to drop my -dcri to 12 to get back to good Eth hashrates. On my Gigabyte Aorus RX 580, I'm at 29MH/s for Eth and 350MH/s for Sia.
Yea I'm using Claymore, haven't used the -dcri command in my bat file though, should I?