All entities are created ONCE in ONE frame. So, no multithreading, no streaming. It doesn't work as it should be.
Not really. I see why this happens for you, but your conclusion is wrong.
You get multithreading, the problem is the worker thread which owns the mutex for too long because of its priority. So the application flow is interrupted because the worker thread owns the mutex while in the meantime the model loading happens.
What you see is a loading in one frame.
I have uploaded a new version which replaces the old one. The only thing changed is the priority of the thread.
Btw, thinking that larger files are loaded slower than smaller files is also not true, assuming that you have a real spinning disk and not a SSD in your computer. Plus: The internal file reading scheduling of your OS might also alter the result.