Don't worry about your hub score.
It's like the stock market: It will go up or down for no apparent reason. The goal of any writer is to focus on posting their best work. Once you hit save/post it belongs to the universe to judge, accept, or reject. It's then time for you to move on to writing your next one. Don't get caught up in the up and down thing because it'll drive you crazy! "Never let success go to your head and never let failure go to your heart."
Note: Most new hubs are automatically rated in the 40s or 50s and they climb up as they are viewed, commented on, voted up as useful, beautiful, awesome...etc. One day you'll have a hub with a 80 score and the very next day that same hub will have 74 while still having the more views and comments than the "new hub" which is now ranked as your best.
(Just be true to yourself and let the chips fall where they may)