Okay, it started to fail again, with 50Gb virtual memory, it started to throw Video TDR failures.
I also changed the PSU for another similar one with no luck.
It was an improvement however, I can mine with 5 gpu for some hours without getting my rig freeze/restarted
With 6 GPU it instantly gets frozen.

I tried to modify straps with Claymore automatic feature, however it throws Video TDR failure when starting.
I will MOD bios to change straps and reduce voltage with AMD drivers, it my final guess.