Barthy

I am mining Aurora, there's some things i am not sure about, why is my actual reward about half of my Calculated expected reward, and why is my PPLNS Score decreasing, i just lost about 3 hours of my PPLNS score, i was watching it one minuet i had 2,605,000 and the when i refreshed i had 2,567,000 which is where i was at 3 hours ago.?