Nook app on android won't recognize epub files on SD card

[AC Question]

I've used the Nook app on my Galaxy Tab 4 for a long time, and always keep the epub files on my SD Card and read them that way. I recently took out my SD card and re-inserted, and now it won't recognize that there is anything other than the 4 books that are already loaded through the Nook app. It did before and doesn't now ... any help on how to get this to work? I'm stumped. (and it's probably something small I'm missing.)