In this case, after I opened the Preview pane and selected a specific post… now all the others are missing from the drop down. And I can’t preview any other pages (there are 15+ others)
That selected post also appears under the Page dropdown, which isn’t correct either.
The only way I can preview a different post is by visiting that post on the front end, then clicking Edit Layout from the CS dropdown. But even then, if I open up the preview pane, it will only offer me that other post.