I don't know if this is what happening or not but....
The bottom of the home screen only holds 50 books, with new books pushing the oldest book off to your library. In the upper right hand corner, hit the options menu and you'll see listed what you were reading last, choose it and it will open it up for you.
Also, look at the bottom section of the Nook where it should have a little open book symbol. Press that at any time and the last book will open to the last page you were reading.
If you want to keep a book from scrolling off the bottom of the home screen before you get to read it, just use your finger to slide it to the upper part of the home screen. It is there now until you remove it. It won't scroll off.
You can also find a book in your library that you want to keep on your home screen even though it has scrolled off. Find the book, hold and press on the book until a menu opens up. Choose the option to place it on the home screen.
I do this to keep the top books I want to read on my home screen so I don't always have to go looking for them. Once I read them, I remove them from the home screen and shelve them.
You can also rearrange the books on the bottom of the home page. Just use your finger on the book and move it to where you want it so books that you can move books to the beginning of the list or to the end of the list depending on how important it is to keep it there.
I actually use my Home page this way to keep most of my "to read next" handy so I don't have to go back looking through the library and shelves. The only thing is that I can't add sideloaded items. But still, I like that home page a LOT!
Hope this helps.
thank you so much for writing all of this! You have completely helped me in so many ways! I couldn't understand why my books kept disappearing (i had over 50, so now i understand) and then i didn't know how to move them back from my library. I was also unaware that the top part of the home screen scrolled! I searched all over the internet trying to find answers and after a few months of nothing I finally came across this post and I am truly grateful, thank you!
try calling customer support