Javascript bug with iframe

I have a page with an iframe: https://demos.port80.services/essency/troubleshooting-guide-e55r/

The plugin is throwing a javascript error, which caused the mobile menu to break on phones. Here is the error:

Uncaught TypeError: Cannot read properties of null (reading 'classList')
    at Object.init (front.min.js?ver=2.1.3:1)
    at front.min.js?ver=2.1.3:1
init @ front.min.js?ver=2.1.3:1
(anonymous) @ front.min.js?ver=2.1.3:1
load (async)
(anonymous) @ front.min.js?ver=2.1.3:1
(anonymous) @ front.min.js?ver=2.1.3:1

If I remove the iframe, the problem goes away.

The content loaded in the iframe is static html, and no javascript is loaded.

Please fix your code so that it works on pages with iframes. Thanks

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