Gallery breaks with update to 5.3. Images show as unordered list

The link above is from a test website posting.
I will include the screen grabs as well from the test site.

Earlier in the week, we upgraded to WP 5.3 and found one ‘update’ error in the theme being used. Fixed that and all was good until I tried to create a new post with a gallery today.
I created a new post, starting adding headers and paragraphs and then added a gallery. In the editor, the preview looks right and as expected. When the post was previewed or published and viewed, the images were full sized and stacked as an unordered list. https://photos.app.goo.gl/tU8MMW529nm8ZWbq7

I removed the gallery, re-saved the post, and repeated. Also tried a gallery on a page. I then went to a site that was not upgraded to WP 5.3 and repeated the process (this test post link). With WP 5.2 and the same plugins as the live site on WP 5.3, I created a gallery and it worked perfectly. https://photos.app.goo.gl/zaeV2wP8JmrnexEK8

I then upgraded the site to WP 5.3 and refreshed the page and the gallery broke.
There seems to possibly be something in the upgrade that breaks it. I am still testing the theme as a possible cause of error.

The page I need help with: [log in to see the link]