Woke up to Fatal error: Call to undefined function et_core_is_gutenberg_active() in /home/accountname/public_html/myurl.com/wp-content/themes/Divi/includes/builder/feature/BlockEditorIntegration.php on line 572 which turned out to be a plugin conflict with Autoptimize.

Here’s how I figured it out

1. I logged into my cPanel to Debug the site. I use the instructions at this URL https://www.a2hosting.com/kb/installable-applications/optimization-and-configuration/wordpress2/debugging-wordpress

2. I followed the error URL to line 572. Not knowing what to do next, I searched for instructions and found this article https://www.isitwp.com/fix-wordpress-fatal-error-call-to-undefined-function/

But nothing worked so I kept looking and found this article https://wordpress.org/support/topic/fatal-error-on-latest-update-5/

Which gave me an idea!

3. I renamed my plugins folder (to plugins2 for example). Created a new folder named ‘plugins’. Reloaded my site URL and found all was well – that is, the white screen and php error log notification was gone – so I began the test.

Instructions for the plugin conflict test

  • Rename your plugins folder (to plugins2 for example).
  • Create a new folder named ‘plugins’.
  • Reload your site URL and if all is well – that is, the white screen and fatal error notification is gone – you can begin the test.
  • Start uploading your plugins one-by-one to the newly created ‘plugins’ folder to see which one is causing the conflict.
  • Delete the conflicting plugin folder from both your newly created plugins folder AND the renamed original.

You do this last step so that when you’re done you can simply rename the newly created testing folder ‘plugintest’ and restore your original folder name to ‘plugins’ as it was meant to be.

Why do I bother? Well, if you have crucial plugin settings like login-redirects or financial-encryptions that will break your site if you try to operate on a whole new plugin, it makes more sense to simply restore the originals in all their glory.