What PSU do you have? 6 cards will need a good PSU, at least a 1000W
Other than that your core clock is too high or core voltage is too low (i.e. too much undervolt).
Try lower core freq or up the core voltage with Wattool 0.92, but dont change anything else
with that tool since it was designed for RX 470/480* cards.
I am running with 2x 750w corsair gold+
I will try that. thanks
Ok, so power should be fine.
In Wattool you will need to change GPU MHz in P7 cell only. Try 1150. Then press Set. And you are done.
Then select the next GPU and repeat. Then watch and see if it becomes stable.
If you want to change gpu core voltage, then for every cell from P0 -> P7, each next value has to equal or be higher than the previous by x times 6.25mV. Those figures are in mV. You can probably assign the value 913 to every cell P1-P6.
Then in P7, try entering 913, then press Set. If it crashes then increase in increments of 6.25mv (rounding to nearest mv will do).