After trying several different approaches, I found that I can run Project (Data Management) on the saved feature class and this will fix the NULL values. The output feature class has the correct Shape_Length and Shape_Area values assigned in the fGDB.
arcpy.management.Project(in_dataset, out_dataset, out_coor_system, transform_method)
It would be great is this could be resolved without having to run an additional data management function. It would also be great if you could just run the Feature Class To Feature Class (Conversion) from a python script for data hosted on ArcGIS Online and Hub.
I am going to put a ticket in for initial issue.