Solution
This issue is likely due to the asynchronous VI and the FGV being called in an Action step being executed in
different LabVIEW application instances. In order for LabVIEW VIs to access shared memory, they must execute in the same application instance.
To ensure that all VIs are executing in the same application instance, you can place both VIs inside of a LabVIEW project. Then, you can specify the LabVIEW Project path in the Run VI Asynchronous and Action step configuration. This will force the VIs to execute in the LabVIEW project's My Computer application instance and the VIs will be able to access shared memory, such as using the same instance of a Functional Global Variable to pass data.