Huge empty space in chrome timeline and gray bar

I'm testing performance of a webpage that is slow. Checking it on Chrome timeline, I see a huge white space before the loading, represented by a gray bar that is almost 2.2 seconds long. I don't understand what this bar represents and what I can do to fix it.

I also see that the page is loaded twice (there are two blocks on the timeline). I would like to understand exactly what does the refresh, because that isn't supposed to happen.