Application module `start` function not called?

That is odd. I don’t know off the top of my head anything that would cause that behavior, though perhaps someone else will think of something.

Given that the behavior is different between environments you may want to comb through the configs for anything that could be different, though again I’m not sure what that might be.

As for your question about what happens when the application starts, it’s described quite thoroughly in the Application docs.