WordPress website hosted in Plesk is not accessible with a 500 or 503 error

Symptoms

• WordPress website is not accessible or some contents of the website don't load. The following error is shown in the browser or in the browser inspector (F12):

  Error 500 external Server Error

  503 Service Temporarily Unavailable

• In some cases, the WordPress Admin Dashboard cannot be accessed with the following error message:

  There has been a critical error on your website. Please check your site admin email inbox for instructions

• In some cases, the website is working if all WordPress plugins are disabled going to Domains > example.com > Click on WordPress instance > Instances tab > Plugins tab:

  

Cause

Coding issue on the WordPress instance caused by malfunctioning plugins, theme and/or customization.

Resolution

1. Log in to Plesk GUI
2. Go to Domains > example.com > Click on WordPress instance > Instances tab > Plugins tab.
3. Disable all WordPress plugins.
4. Enable WordPress plugins one by one and check the website accessibility until the problematic plugin is found.
5. Enable all non-problematic WordPress plugins.

   Note: Once the problematic WordPress plugin is identified, contact WordPress plugin developers and change current PHP settings if required.

6. If this did not fix the issue, verify the following:

   • The installed WordPress plugins are up to date

   • The installed WordPress plugins are compatible with the other WordPress plugins

   • The installed WordPress theme is up to date

   • The installed WordPress theme is compatible with the WordPress plugins
   • Both WordPress plugins and theme are compatible with the current PHP version and PHP configuration