We created an 'escalation action' in SOI using the $[Host Name] property to pass to an email. The hostname value is not the same as the one we see in the SOI console.
The $[HOST NAME] property is valid only for CIs that are hosts, and you may have CIs that do not have the host information at all in the instance ID in which case we shouldn't use it. The $[Model Name] is the name you see of the alert in the SOI console.
You need to change the property to be passed to $[Model Name] instead of $[Host Name].