NextGEN Gallery – can't navigate to the next photo

When I click on an image in an album, it opens but I can get to the next photo. The arrows are missing. I’ve followed all of the usual suggestions (everything up to date, default template, disable all other plug-ins, etc). I don’t know what update this occurred on but I have updated several times since and the problem still exists. I had the problem on another site years ago and it corrected itself but this one has not.

You can see the effect here – https://ussbrownson.com/blog/?page_id=558