After being here for 3+ years, I would say the fluctuations are normal. They go up and down and cannot be linked to one discernible action or set of actions.
Think about it-- If anyone really knew the 'formula', they could 'play' the system, and the scores would be meaningless. (They are almost meaningless anyway. They have little or nothing to do with earnings, for instance.)
My guess is that the 'formula' determining ups and downs is inconsistent, but I think people do tend to settle into a certain range of scores, after awhile.
On the other hand, I have no idea.