I don’t know when they disappeared, but I assumed it was when I installed Custom Sidebars, however from that support forum, he is saying his plug in wouldn’t cause it to disappear.
A plugin called “White Label CMS” turned off the Screen Options. I was using it to customize the black navigation bar at the top of the website for signed in people. So Custom Sidebars removed the sidebar settings I was after and White Label CMS removed the option to apparently turn that back on.
That is the plugin. I have no idea why sidebar layout was unchecked in screen options. The plugin White Label CMS then turned off the ability to see screen options and so I was stuck. Now that I’ve turned it back on, the sidebar functionality is restored and I’ll have to search for another plugin for the white label functionality.