After you enable hotlinking and the hrimg image proxy, your gallery lightbox links may still open the original full-resolution images instead of the proxied versions.
Why this happens. The image optimizer plugin rewrites rendered image source attributes automatically. Gallery lightbox links come from a separate binding in the page builder, and the plugin does not touch them.
What to do. Configure both the plugin and the lightbox binding in the page builder so the proxy covers the full gallery experience. Once both are set up correctly, lightbox images load through the proxy at the appropriate size, which typically reduces the image file size substantially.