One MSI rx 580 running at 11 mh/s

I have two identical rx 580 – both on stock bios. One gets 14-15 MH/s @ 120w the other 11 @ 120w

Both have the same overclock, and I’ve tweaked it to allow more power to try and compensate. But even with more power, higher clocks / memory I get the same or worse. I’m completely stumped

Both have Samsung memory, and is installed in a b450 board, but I don’t think bandwidth is an issue.

The problem follows the card if I switch or swap the two identical cards. Any help?