Since the updates to the right sidebar there is now a <div class="js-sidebar-zone" ..., which on other sites seems to work as intended; however, with the new homepage on Stack Overflow, it comes with the minimum height set to 300 pixels:
<div class="js-sidebar-zone" style="min-height: 300px;">... </div>This results in an empty space between the other sidebar widgets and recently viewed posts:
