I would remove the -pll 850 parameter. I am getting appropriate hashrate without using the -dualminer-pll parameter, and I have noticed instability when using this parameter on previous versions of cgminer. Regarding your invalid nonce error, I get those too occasionally, though you should see less once you drop your pll parameter.  Are you mining over a wifi connection? This would be the next thing I investigate if removing the non-necessary parameters doesn't help and you are using 9 DMs per p10-u2.