I have the same issue and it affects both, left and right sidebars. It baffles me because I get it with the most happy day scenario - I just generate the most basic skeleton with yo theme generator with all settings defaulted (ftl templates, styled base theme). At first I also though it's a styling or javascript problem, but after a brief analysis I found out that the side bar is not present in the markup at all, which seems to be intentional, especially when there are no errors in the server log. At this point I'm really not sure if it is a bug or a feature. If it is a bug, then it is a showstopper bug in the most common usage in a GA release which would be insane irresponsibility of Liferay QA. But if it is a feature and theme developers are expected to pull sidebar content from server themselves somehow, I would expect it to be thoroughly explained, because it would have to be done by every single theme developer, since Liferay is useless without it's sidebars.
One more interesting detail. If I turn on a sidebar on another page which has the classic theme and I return to page with my theme, then the sidebar is visible, but the problem is oposite - it won't hide. After clicking the hide button, the page content widens to the full width, but sidebar stays in it's place so it covers part of the page which is under it. This assures me that this is systematic problem and not some accidental bug.
I have also noticed that when I click on sidebar toggle button in classic theme, it fire ajax request bearing info about visibility of sidebar. No such thing happens in my theme.
