The tag property .AlertCurrentState is not updated when a new alarm occurs. It will be updated when the alarm is acked though. I noticed this when upgrading from 7.5.10 to 7.6.3. My project’s screen icons that used this property to show alarms stopped working after the upgrade.
This issue is fixed for Ignition 7.6.5
It’s baaaaack! 
This exact same issue is occurring in version 7.7.5 for us. AlertCurrentState is always None until the alarm is acknowledged.