Check GPU load in gpu-z (must be 100% all the time).
I will do some tests in 1-2 days to confirm that the miner produces correct number of shares, though I already did it for v11.

UPD: It seems I found the reason, when pool sends new job, v11.0 drops old job too late (loses 1-2 sec). I have fixed this bug but it will take 1-2 days to test it properly and release an update. However, you can test a fix right now if you want and tell me if it helps:
https://mega.nz/#!TlYQAJSZ!291Swk4GbJLC5JYmax_fc-tLWjfwKsFTnOUSVGqsDlA