Having recently gone through this process, I did get to an application. I did not understand why it was rejected. It turns out there were some wording issues in one part of the response. My first course of action in the rejection letter was to go to the Public Service Commission. They told the hiring manager to give me further feedback. I got further feedback. I went back to the Public Service Commission and they said I got further feedback and that's it.
From there I went back to the Department of National Defence. They put me through to VPSU. I was unaware that this unit even existed before then. I had conversations on how I had to wordsmith my submissions to a point that I didn't even understand what I was applying for. That was my process.