This is an expected behavior in VMware vCenter Server and VMware vSphere Update Manager.
In the event that VMware vSphere Update Manager downloads a critical notification alert from the VMware patch repository, the VMware critical notification alarm is triggered for VMware vCenter Server to alert you to review the critical notification alert details.
To review the notification alert details:
- Log in to VMware vCenter Server using the VMware vSphere Client.
- Navigate to Home > Update Manager.
- Click the Notifications tab for more details about the Alert/Notification.