Odd situation.
Have a rig with 3 x RX570 4GB. Was getting 27Mh/s with Claymore 10.6.
Had to change rig to different board and hard drive. Board is the same, hard drive is slightly different (slower, but didn't think this mattered).
Same amount or RAM *GB, same pagefile, 16GB, same divers, same version of windows but now only getting 20Mh/s.
ANy ideas? Really frustrated.
Memory Clock - 1750 MHz
Core Clock - 1244 MHz
Check for compute switch in the driver, by default it is NOT set to compute.
You can try much higher mem clock. It is usually safe to try 2150, even more for select cards.
I have experienced performance degrade when undervolting fail to set up, but not that much really. Check actual core and mem voltages and try to set to 950 mV and lower.
Go one at a time and check for results.
27 is pretty low for RX570, try to find better bios settings.