are u using modded bios ?did you saved your cards original bios file for each cards ? , card 1 - bios 1 , card 2 - bios 2 , card 3 - bios 3 ....
those cards can have a different bios version , just like the RX 480's ...
did you flashed the sapphire nitro rx 570 nitro + 8 gb OC bios or silent bios ?
reset all overclocking settings if you used any , watttool , wattman , afterburner ...ect
flash back the original bios for your cards , i hope u was smart enough and saved all
.
orthose sapphire nitro rx 570 nitro + 8 gb should have a dual bios , switch the bios switch for each cards to the opposite way and try mining .
the 1200 watts psu might not enough if you dont know how to overclock the mem without proper undervolting ,and underclock , undervolt the gpu . rx570-580 cards in some stress test can pull 180-200 watts easy , mining with those cards are a real stress test , torture
also...
when you asking for help , the full system spec would be great including OP system , driver version
what happening if you mining with 2, 3, 4, 5 cards ?