Resolution
This is a known issue, and is currently being reviewed by VMware.
If alarm actions are configured to send a notification email or SNMP trap when the alarm status changes from Yellow to Red, an unreasonable amount of false alarms could be generated in environments where hosts are frequently entering and leaving the standby mode.
False alarms can be identified with a second notification when the alarm status changes back to Green (if the host connection is successfully restored). To revise the first triggered notification (Yellow to Red) by a second notification (Yellow to Green), you must adjust the trigger and frequency of the alarm.
If changing or disabling the alarm actions is not an option for you, use this workaround to quickly identify false positives by adjusting the trigger and frequency of the alarm:
Navigate to the object where the alarm is defined (the default is the vCenter Server).
Click the Alarms tab, then select the Definitions view.
Right-click the Host connection and power state alarm and select Edit Settings...
Click the Reporting tab and set the Frequency to 0 (zero) minutes. Do not modify the Range value.
Click the Actions tab and enable the Yellow to Green trigger for the desired alarm action (usually email or SNMP notifications) by selecting Once from the list.
Click OK to save your changes.