I have been having a problem with a few of my books that the cover art is not showing up on my Fire HD. Oddly it's only a few, so it's very puzzling why certain books changes while others do not. I have formatted Mobi to Mobi, Mobi to Awz3, everything and not even the original art is showing. It's just a blank square with the word Kindle on it. My program is also updated to current version. I like to have covers somewhat match when it's from a series.
