Only loading 2 images in popup

I have a gallery section that is based on the following layout:

<a href="url.com/wp-content/uploads/collage1.jpg" rel="prettyPhoto[galleryname]" class="hs-rsp-popup" data-slb-group="2639" data-slb-active="1" data-slb-internal="0"><img src="url.com/wp-content/uploads/logo.jpg" alt=""></a>

<a href="url.com/wp-content/uploads/collage2.jpg" rel="prettyPhoto[galleryname]" class="hs-rsp-popup" data-slb-group="2640" data-slb-active="1" data-slb-internal="0"><img src="url.com/wp-content/uploads/logo2.jpg" alt=""></a>

<a href="url.com/wp-content/uploads/collage3.jpg" rel="prettyPhoto[galleryname]" class="hs-rsp-popup" data-slb-group="2641" data-slb-active="1" data-slb-internal="0"><img src="url.com/wp-content/uploads/logo3.jpg" alt=""></a>

But when I click on image 1 or 2, the popup gallery only shows the first 2 images, not the 3rd, 4th, etc… If I click on the 3rd image, that image will appear in popup but gallery arrows will then only let you access the first 2 images.

Any idea why this might be happening? Dev site is at 173.254.96.82/ ~ evianspr/ (remove spave before and after ~

https://wordpress.org/plugins/really-simple-popup/