Good pattern
· Open the attached project.
· Open the Level blueprint.
· Make sure that it is connected to the Add Nav Modifier component.
· Execute in PIE.
Result: NavArea_Null works and enemies are not here.
Bad pattern
· Disconnect the Add Nav Modifier component with Level blueprint.
· Connect Add Nav Link Component and start playing.
· Set area class for adding navigation link component to NavArea_Null.
· Execute in PIE.
Result: NavArea_Null does not work (enemies come here).
Expect: NavArea_Null works and enemies are not here.
Both patterns can be confirmed with the console command: Show Navigation.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-58155 in the post.