Update:
Putting Gen2 to all pcie slots
DDU in safe mode and installing combined drivers again
After 2-3 restarts that when starting claymore it was loosing every other time one-two cards from mining and hashes, it started mining with all 6 of them.It mined about 8-10 hours and crashes with hang error in a card.After restart started mining again and then hangs with another card.Mysterious.....