I think there is not enough power and your psu just shutdowns
because sometimes amd settings for downvolting are not applying. and it necessary to move the clock slider in afterburner and then hit apply and here we go voltage is now correct, so maybe you could check there?
I don't think it's that. I'm using overdriveN, and even if they all reverted to stock voltages, the draw on cryptonight would still be less than 1000W on the second PSU.