I have an extensive ebook library aside from what I've purchased via Amazon, and I use Calibre to keep it organized. It's always worked flawlessly. However, a few days ago, I noticed something that has been bothering me quite a bit (I'm a tad OCD on organization

).
Right now I'm reading through a Star Wars series of mine. It's called Legacy of the Force. There are 9 books in it. In Calibre, I set it up so they would show up in order on the Kindle as opposed to how they would be sorted by default (by random title). They look like this:
Star Wars - Legacy of the Force - 1 - Betrayal
Star Wars - Legacy of the Force - 2 - Bloodlines
...and so on. In fact, I have several very long series on my Kindle (Harry Potter, Song of Fire and Ice, more Star Wars and Star Trek series) that I use this method with. It's worked perfectly up until now, in which it just displays at random for no discernible reason, after no action of my own. I finished the 5th book in the Legacy series, so I went to open the 6th. It was not after the 5th. After the fifth was this:
Star Wars - Legacy of the Force - 7 - Fury
Star Wars - Lost Tribe of the Sith - 4 - Savior
...and it continues with increasingly bizarre choices, including earlier volumes of Legacy, and other Star Wars books that begin with letters before L.
Long story short, my books are appearing all sorts of out of order, and I have no idea why. Anyone else have any ideas? On top of that, any idea why a certain book would just be missing when it's in the Kindle's files when connected to my computer, and Calibre shows it as in my library and device library? I'm sad and confused.

Thanks in advance for any help!