The Nav Mesh is appearing in the editor, but not appearing during PIE when its Z value is set to a size similar to the floor size that it is generating on.
Making the Nav Mesh Bounds Volume taller resolves the issue.
The licensee has also provided a test project showcasing the issue which they've linked in their thread.
Result: Nav mesh appears in-editor but does not appear during PIE
Expected: Nav mesh would appear in PIE as well as in editor.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-41709 in the post.