SITE BROKEN: Home page coming into The Content rather than desired posts

We’re attempting to create a Blog Single template. It was working as of last week. Now it’s not. When adding a Blog Single template now, the “The Content” (the_content()) is displaying the home page, not a post. Nobody knows what changed about this over the weekend. it just started doing it.

This was a fresh install and new site, so we’re not inheriting any stuff from an old site. We do have ACF Pro installed on the site, but it was working fine and not causing any conflicts.

One thing we just discovered is that if there are no published posts, The Content defaults to showing the home page. That leads to the question of how do we edit a draft post content’s layout directly in Cornerstone if it has to be published to edit it? By the way, we’re not going the usual route of editing the post content in the Block Editor for inclusion in the template. We want greater creative control over the content via Cornerstone (even though we know that it breaks the usual WordPress model of keeping content and template separate in blog posts so we don’t end up with shortcodes in the content).