After upgrading to Aria Automation 8.18.1 Patch 3 there has been a change in the Custom Properties.
Workflows or scripts using the externalId are failing due to being unable to find a externalId.
Custom Property on all objects 'externalId' is missing after deploying a VM through Aria Automation. This property was seen in other versions previous to this.
Aria Automation 8.18.1 Patch 3
The property externalId was replaced by resourceId within the custom properties.
This is a known issue and will be resolved in Aria Automation 8.18.1 Patch 4
Workaround