WordPress notifications are received: Failed to reset cache for the instance #902: An error has occurred when decoding JSON: Decoding failed: Syntax error

Symptoms

• WordPress email notifications are received by Plesk admin. A similar error can be found in /var/log/plesk/panel.log when clicking on Plesk > WordPress > example.com > Refresh.

  Website Example (https://example.com): Failed to reset cache for the instance #902: An error has occurred when decoding JSON: Decoding failed: Syntax error

• Cloning a WordPress using WP Toolkit fails with the error:

  Failed to reset cache for the instance #902: An error has occurred when decoding JSON: Decoding failed: Syntax error

• Attempt to get theme/plugin list will print PHP code instead of JSON list of themes:

  # plesk ext wp-toolkit --wp-cli -instance-id 902 -- theme list --fields=name --format=json --quiet --skip-themes=false | head

  ---

  # plesk ext wp-toolkit --wp-cli -instance-id 902 -- plugin list --fields=name --format=json --quiet --skip-plugins=false | head

Cause

Plugin or theme are not compatible with wp-cli.

Resolution

Contact the plugin or theme developers for assistance.

Note: in case the Elementor plugin is in use or Elementor-related errors in logs, refer to this article.