Jamie

This issue is unrelated to Beaver Builder. It is instead related to your theme, Astra, and CSS they are using.

.ast-menu-toggle:focus {
    outline: thin dotted;
}

You’ll need to reach out to the Astra team for assistance.

Unfortunately, not with certainty as we’ve never been able to replicate it.

We’ve only seen this a small handful of times.

In some cases, the cause can be a tiny increase in memory usage when the page is set as the home page. So in that case, increasing the memory limit might work.

In others, users have found that turning Zlib on works.

In other cases, a workaround was not found other then unsetting the page as the home page.

There are various possible reasons why this could be occurring.

– Plugin conflict

This may be a plugin or theme conflict. Please attempt to disable all plugins except Beaver Builder, and use one of the default (Twenty*) themes. If the problem goes away, enable them one by one to identify the source of your troubles.

If you can install plugins, install and activate "Health Check": <a href="https://ww.wp.xz.cn/plugins/health-check/">https://ww.wp.xz.cn/plugins/health-check/</a>  
It will add some additional features under the menu item under Tools > Site Health.
On its troubleshooting tab, you can Enable Troubleshooting Mode. This will disable all plugins, switch to a standard WordPress theme (if available), allow you to turn your plugins on and off and switch between themes, <strong>without affecting normal visitors to your site</strong>. This allows you to test for various compatibility issues. 
There's a more detailed description about how to use the Health Check plugin and its Troubleshooting Mode at <a href="https://make.ww.wp.xz.cn/support/handbook/appendix/troubleshooting-using-the-health-check/">https://make.ww.wp.xz.cn/support/handbook/appendix/troubleshooting-using-the-health-check/</a>

– JS error coming from custom code added to the to a module like a script embed to an HTML module, etc.
In this case, please try to see if safe mode works: https://docs.wpbeaverbuilder.com/beaver-builder/troubleshooting/debugging/safe-mode/

– Reaching server limits, such as memory limit (most common).

Since this is happening only on one page, this is a real possibility. Revisions might be pushing you over the memory limit. You can try loading the page in BB without loading the revisions temporarily by adding &norevisions to the URL. For example:
yoursite.com/sample-page/?fl_builder&fl_builder_ui&norevisions