Default [gallery] shortcode not working, but the TagDiv Gallery is.

I’ve tried disabling ALL plugins, and the default [gallery] shortcode is still not working. If I revert the theme to Twenty Sixteen, then the gallery shows just fine.

Additionally, if I specify the gallery to be a TagDiv gallery, it does show up.

Any ideas on why this could be happening?

Thank you in advance for your help.

For your reference, the page I am using to try this out is: http://newest.radass.com/galleries-people-human/

First, I disabled ALL plugins, except the S3 Offload, since all of our assets are on S3 storage. (Note, even when I disabled these plugins too, the Gallery html was not generated.)
Plugins: https://drive.google.com/open?id=0B2QpbwncFqR9d2FyV3FMUWdnR1k

Next, I added a standard gallery to a new post. Here, I show both the visual and text editor.
Text Editor: https://drive.google.com/open?id=0B2QpbwncFqR9RVJJWHdUS29oNjA
Visual Editor: https://drive.google.com/file/d/0B2QpbwncFqR9YVVQX0xfM25aRDg/view?usp=sharing

Now, looking at the Post page, the gallery does NOT render out. Using Developer Tools in Chrome, I’ve verified there is no Gallery being rendered here.
Post: https://drive.google.com/open?id=0B2QpbwncFqR9UG0tMFJzN0hMVUU

However, if I edit the gallery, and ask it to use the TagDiv slider:
Gallery Editor: https://drive.google.com/open?id=0B2QpbwncFqR9VkdXSVRZRXR0RTg

Then it will properly render THAT gallery out.
Post: https://drive.google.com/open?id=0B2QpbwncFqR9WXlJTDg3NnowclE

Again, if I change the theme to Twenty-Sixteen, the Gallery shows up no problem.