Mmmmh, it's been a while since I did some programming in Leadwerks, and things seem to have changed slightly... If I see this right, for C++ projects the Main.lua script is executed in App::Start(), which contains the game loop. And when this is ended, the C++ execution continues in App::Start(), then App::Loop() (which basically does nothing). Also, since everything is done in Main.lua, the World, Context, Camera and Window member variables are all null.
I can change this according to my needs, but I think for C++ projects there should be a template with a clean lifecycle implementation done in C++. When I choose a C++ project, I prefer to use Lua for encapsulated entity behavior, but use C++ for the heavy lifting in the background.