expand-button-hidden duplicated many times

I’m running the latest (3.7.0) version of the plugin.

The issue is that the button (with class=”expand-button-hidden”) to expand the image from the gallery gets duplicated anywhere from three to dozens of times.

Here’s the screenshot of the issue.

Here’s how the generated HTML looks like.

Any idea what could be causing this or how to debug this?
Here’s the URL to a page where this happens.

I cannot try only using the default wordpress theme with your plugin because we don’t have a preproduction environment, and I can’t just revert to the default theme with no other plugins in production. I would still appreciate your help. Thank you.