The Arrows on the bottom are not supposed to change the Large image that is displayed.
the arrows on the bottom are to advance through the thumbnails. The gallery in your link has 19 images, it only shows 10 thumbnails at a time. to see the additional thumbnails, use the arrows at the bottom
To change the large image, either click a thumbnail or use the next / previous arrows at the top.
for the other gallery, I'll need to troubleshoot directly, see the private message section.