Unable to log in to the WP Admin dashboard by using WP Toolkit: JSON: Illegal Token

Symptoms

• Unable to log in to the WP Admin dashboard by using WP Toolkit at Domains > example.com > WordPress tab > Log In button:

  An error has occurred when decoding JSON by Zend_Json: Illegal Token

• Same error is displayed in during the following operations as well:
  Domains > example.com > WordPress > Updates > Check for updates
  Domains > example.com > WordPress > Clone

• The following log is found in at /var/log/plesk/panel.log with Debug enabled:

  DEBUG [util_exec] Finished in 0.6062s, Error code: 0, stdout: "https://www.example.com/wp-login.php"
  PHP: [notice X 0][/var/www/vhosts/example.com/httpdocs/wp-content/plugins/elementor-pro/modules/loop-builder/module.php::200] strpos(): Passing null to parameter #1 ($haystack) of type string is deprecated [array (
  'trace' => '
  0: ElementorCoreLoggerManager -> shutdown()
  ',
  )]

• Logging into WordPress Admin Dashboard is working as expected using the native WordPress login functionality, e.g. https://example.com/wp-admin

Cause

WP Elementor bug, which was reported to the plugin's developers by the Plesk team.

Resolution

Resolved in Elementor in v. 3.12.3 by it's developers.