Plesk can not be updated or is not accessible: Class LaminasServiceManagerServiceLocatorInterface cannot implement previously implemented interface

Symptoms

Plesk update fails or Plesk panel cannot be accessed with the following message:

PHP Fatal error: Class LaminasServiceManagerServiceLocatorInterface cannot implement previously implemented interface PsrContainerContainerInterface in /opt/psa/admin/plib/modules/monitoring/vendor/laminas/laminas-servicemanager/src/ServiceLocatorInterface.php on line 18

Cause

The outdated version of the Monitoring extension is installed on the server.

Resolution

1. Connect to the server via SSH/RDP.

2. Update the Monitoring extension to the latest version with the command below in the SSH console or CMD/Windows Powershell:

   # plesk bin extension --upgrade monitoring