Hoangle1523, I had absolutely the same issue with my RX580 cards.
You should reset settings in MSI Afterburner (set only for fan speed) and use settings in Claymore (sure if you mine with Claymore), as example:
-cvddc 950 -mvddc 950 -cclock 1150 -mclock 2100 -powlim 30 -ttli 75

It gives me 29 Mh/s instead of 27Mh/s with default settings, memory Samsung and Hynix.