One page at a staging site does not display the left sidebar. Inspecting the source code shows that there is no <div… class=”… left-sidebar”> for the page. Other pages show the left sidebar. Sidebar Debug shows the Primary & Secondary sidebars shifted to the left. This causes text in the right sidebar to overlap page content.
The page is configured in the Main Menu as the first page in the Connection menu. Other pages in the Connection menu have a left sidebar that includes as its first item a link to the Connection page.
I’ve seen this thread that suggests there is some mechanism other than configuring the Main Menu to have a page appear in the left sidebar. I have found no settable feature of the Connection page that places it in the set of pages that display the left sidebar.
Another case of autopedicide (shooting oneself in the foot). In chasing down what turned out to be a missing double quote in an email link the original Connections page was trashed. One feature of the left sidebar is that it requires at least one page to call Connections its parent. Which makes sense. When Connections menu pages had their attributes set for parent = Connections all was good.