Thanks Pavel, yes that's the one, the page refresh loading bar.
A colleague has helped me using The Performance tab Dev Tools in Chrome, and we've actually determined that it's not the loading bar itself, as we previously thought, it just happens whilst the page is reloading.
He thinks that as the css for the Queue headers (Open, My Tickets, Closed etc) is reloaded they briefly lose their padding amongst other things, resulting in the page shifting, as shown in the screenshots.