I found out that the javascript files that handle this functionality were omitted for some reason. I disabled all the plugins and got rid of all my custom scripts but none of these helped. There was something either in my header.php or page.php file that screwed things up. I still don’t know the culprit; but luckily, I saved a few old copies of the files and was able to revert to where the feature worked properly.
Thanks royho for the reply.