Thank you for all of the responses!
The black stripe is covering part of the bottom of the image so it's not an additional blank space that is being filled in. All of the images in this series are squares, so I can drop in another image into the same slot without changing any print settings or slot size, and that image will print fine.
I'm going to re-process the image from the original raw file today and see if that fixes it. Maybe something in the file is corrupt...