I’m not going to lie, Critical Errors are kinda the worst type of errors to deal with cuz it’s never really a straightforward fix but there are procedures for finding the cause. First is the standard procedures
- Change the theme
- Disable all plugins excluding required plugin
This is kinda the easiest way to see if there are conflicts and the easiest way to debug. Once you find the plugin with the issue it’ll be easier to debug. Usually, as a support role, you’ll tell the customer to reach out to the conflicting plugin
If you don’t have admin access, log in via FTP or your hosting’s file manager and rename the plugin folders until you can access the admin site. From this, you’ll know the plugin with issues.
Method 2:
CHECK YOUR LOGS, if you don’t know how to enable error logs read here: Enabling the WordPress Debug log – DreamHost Knowledge Base
Once enabled replicate the error and look at the log file. From there it’ll probably spit out where the error was found, it could be a bad code/missing parameter or something else, you can pass this information to the plugin’s or theme’s dev theme. This information is valuable since it makes their job easier.
Method 3:
If you found your plugin, and it has multiple features. Disable them one at a time, there’s a chance that it’s a specific feature that’s causing the error. For this it’s likely a bug so make sure to raise it in Git or Asana or whatever you use to raise bugs.
Method 4:
Simply re-install your plugin. Sometimes it just happens that the installation or update went bad and reinstalling/clean installing the plugin fixes the issue.
Method 5:
Just resave the setting, I know this sounds dumb but believe me. Sometimes plugins are stupid and it doesn’t save the setting properly, so fix it by disabling the feature -> Save -> Enable feature > Save