It's normal for the Hub score and the Hubber score to fluctuate. There are many factors that come into computing these scores. For example, in a hub's Hub Score, the length is taken into consideration as well as the uniqueness of the content. For the Hubber Score, some factors include your participation in the forums and the collective Hub Scores of all of your hubs.
For more detailed information about this, check out the HubPages FAQ on hub scores as well as the learning center guide. Here are the links: http://hubpages.com/faq/#how-to-improve-hubscore and https://hubpageshelp.com/features/Learning-Center-... . Hope this helped.