I have changed the thermal paste and memory pads several times. Cleaned the heat sink thoroughly and replaced the fans, but still the same problem.
I saw several times where the wrong setting of heat sink after changing thermal paste and pads caused high temperature on GPU's. You should need to be sure that the heat sinks 100% leaning on the GPU chip. you must not put a thicker thermal pad than is a gap.
7x rx580 consumption the only 580w? Are you sure? This is from mining software, right? did you measure before the complete miner machine?
This is only the consumption of video chips from 7 video cards. There are no such results. Such a farm consumes about 900 watts or more from the wall.
Each miner must have a wattmeter in order to check the correctness of the settings and not set lower consumption values, from which the power consumption from the wall does not change, but the video cards start to fail.