[Plugin: NextGEN Gallery]: New images not appearing in existing gallery

I’m using the gallery shortcode –[nggallery id=3]– to display a NextGEN gallery on a page. When I add a new image to the existing gallery, the new image is not displayed with the rest of the images UNLESS I am logged into the site as an administrator. If I’m not logged in, the new image is not displayed; if I’m logged in, it shows up perfectly.

Why would this happen?

You can see the problem on: https://litcrawl.org/nyc/get-involved/become-an-author-sponsor. (As a workaround, I’ve added the new image manually–it’s the first image shown.) If the gallery were working properly,you’d see 6 book covers on this page.