Hi and thank you for you words,
That happens to me too. I dont know why, but when you get a lot of GPU RX580 in one simple motherboard with differents settings, some times one of them drops the wattage. I think is not the VBIOS flash you are using, maybe that one needs some special adjustment (Try playing with low or high voltage). In my case, I put it on another worker with different settings and works fine.
I get less Mh but work for me …