Hi so i have found finally the real problem.

One of the GPUS in the rig is not "broken" because it can work fine in gaming and other applications but it cannot sustain the constant heat/pressure of the mining process so after a while it crashes and brings the whole rig down.I suspect that this GPU has a lower quality than the other 5 gpus in the rig.

I changed this GPU and everything started to work fine.

Problem SolveD!