Nativized widgets that include a custom button cause a crash if Event Driven Loading is enabled

Nativizing a Blueprint that includes a custom button (a Blueprint parented to the "Button" class) causes a crash when Event Driven Loading is enabled. Disabling Event Driven Loading can workaround this issue.

Regression?: No
This occurred in 4.19

1. Download the attached project
2. Package the project for Windows 64
3. Open the packaged project
   Result: The game crashes due to an assert (see description for details)
   Expected: The game opens successfully and displays the button