The issue typically occurs when external values take a long time to populate and subsequent fields have dependencies.
When the form opens a call is made to populate external values.
If any fields are selected before this call completes the fields will be blanked once the call is returned.
Aria Automation 8.18
The issue is occurring due to the absense of a loader functionality. It occurrs when a call is taking a long time to execute which clears the already selected form values once complete.
A resolution for the issue is planned in the ServiceNow plugin version 9.1