Nav Area class is reset after updating from 4.19.2 to 4.20 Preview 3

When upgrading a 4.19.2 project to 4.20 Preview 3 the Nav Area Class is changed to None instead of the value it was before the upgrade. Upgrading from 4.18.3 to 4.19.2 works as expected.

This was tested in 4.20 Preview 3 (CL-4135216) and Main 4.21 (CL-4151283)

1. Create a Blueprint project using the Empty template in 4.19.2
2. Add a Nav Mesh Bounds Volume to the default Level
3. Create a Blueprint based off an Actor and add a Collision Box to it
4. Select the Collision Box and check 'Dynamic Obstacle' under Details>Navigation
5. Make sure the Area Class is set to NavArea_Obstacle
6. Save the Project
7. Open a copy of the project in the 4.20 Preview 3

Results: Nav Area Class is reset to "None" from "NavArea_Obstacle" after project update to 4.20 Preview 3.

Expected: Nav Area Class is still NavArea_Obstacle after update.