You are using Nagios for your sentinel monitoring. The disk usage is at 100%, but you didn't get a notification alert from Nagios. It seems all notifications from Nagios have stopped.
Nagios system state could be overridden to downtime to prevent false alarms in case of network connection loss. Downtime notification should be returned to the reporting state. Please contact the Customer Support team to check the Nagios system, and we will get back with the root cause and solution.
The agent should elevate the ticket to the Professional Services team to repair Nagios sentinel alerts.