Plesk intermittently provides error when opening different pages: Syntax Error: Unexpected token ‘<‘ “<!DOCTYPE> ” is not valid JSON – Plesk

Symptoms

• Intermittent error in Plesk when opening different pages: Syntax Error: Unexpected token '<' "<!DOCTYPE> " is not valid JSON

• Sometimes the following error also could be shown: ApolloError: Response not successful: Recieved status code 500

• There are no related records in %plesk_dir%adminlogsphp_error.log log file.
• All Plesk components are up-to-date and there are no corrupted files. Checks with Plesk Reconfiguratior are passed successfully.

Cause

Some pending Windows updates require the server to be restarted.

Resolution

Restart the server.