I can't understand: if dag verification fail, it's mean a hardware error here,
Is there have any meaning? The card could make a lot invalid shares, the hash rate of pool will be bad.
No. Because the dag creation is a heavy process for the gpu that fails on the highest clocks. But to solve the hash is an easier task that can be done on high clocks. So that meens that you can increase the mem clock and still get 100% accepted shares. I have tested it on the 3070 and 2060 and it works. +200-300 mz stable