my ASUS STRIX rx570 4gb cards, wouldn't go more than I=29, hashing at 500~600 H/s, no matter what clock and memory settings I put in AB. what can be the problem?

at the same time, some of my RX470 8gb nitro+ are hashing at I=50 and 850-950H/s on one rig, and I=41 and 750-800H/s on the other..