I just started using the theme (and love it!!), and was having a similar issue that was addressed in an earlier post about the sidebar having too small a width (which there was a temporary CSS workaround for), and now since updating to the newest version of the theme, I started having this exact same problem with the sidebar disappearing. Please help!
I noticed that after the theme upgrade, there are now two sidebar widget areas: 1 for posts and one for pages. Your original widget area is now for posts, but the pages widget area is empty by default. Copy your posts widget settings into your page sidebar widget settings, and your page sidebars will return.
Thank you! That solved the problem.