Warning: Invalid argument supplied for foreach()

I randomly get the following error that brings down the entire site:

Warning: Invalid argument supplied for foreach() in /path/to/wordpress/html/wp-content/themes/enfold/config-templatebuilder/avia-template-builder/php/template-builder.class.php on line 132

Fatal error: Call to undefined function post_has_layerslider() in /path/to/wordpress/html/wp-content/themes/enfold/config-layerslider/config.php on line 157

• It happens for no reason (no changes made to the website before this happens)
• Not a cache issue, as it happens in incognito mode as well
• The site is running on a child theme with its own style.css and functions.php
• Other websites of mine running Enfold do not encounter this issue
• I can “fix” the issue by navigating to http://www.domain.com/wp-login.php, all of a sudden now when I go to the website it works
• This has happened several times in the past

I’ve included the domain (private content), but by the time you see this it will likely have fixed itself. I’m raising this as an issue since it is not the first time I’ve seen this, and a quick Google search shows numerous other sites that have been indexed with that same error:
https://www.google.ca/search?q=Warning:+Invalid+argument+supplied+for+foreach()+in+enfold/config-templatebuilder/avia-template-builder/php/template-builder.class.php+on+line+132

I’m hoping you can shed some light on:

• Has this been seen before?
• Is there a known fix?

Thank you for your ongoing support! I am a big fan of this theme.