I'm using "Gallery" for the first time. The small gallery bar works fine for me except that most of the thumbnails are not displaying thumbnails, but instead just a small section of the chosen image.
The other gallery doesn't display at all, though I have filled out most of the parameters and listed 8 image files.
The Small Gallery Bar reduce the size of your images to display them in the bar, then increase their size when clicking on them.
When you decrease the size of a big image then yes, there may be a bug, and the display is then a part of the original image.
The only way to solve this issue, is to set a smaller image in the gallery.