I use highlighting for recording any peculiar passages on my NST and in lieu of bookmarking. Since the Contents|Notes & Highlights only shows several words, I sometime fiddle to select the important words at the beginning.
Recently I found that Contents|Notes & Highlights contained a blank entry that directed me to a page without highlights. There is no way of deleting such an entry because there's nothing to select. As I made further selections, I noticed that the page number for the blank entry in Contents|Notes & Highlights eventually listed out of order by one page.
Worse, I began to find future highlighting less than reliable: ocassionally pointing to the wrong highlight with some highlighted text not even indexed. Powering off the Nook seemed to fix this problem, but the problem soon recurred with future highlighting. Unfortunately, powering off had no impact on the blank entry in Contents|Notes & Highlights.
I suppose I could have cleared all Notes & Highlights but I had too many highlights to lose and, of course, there is no backup. What finally seemed to work was highlighting words, by trial and error, either side of the the blank entry in Contents|Notes & Highlights. Once I managed to trap the empty highlight between consecutive words, the blank entry vanished in Contents|Notes & Highlights!
I hope this helps someone.