Okay, this has happened enough times, I've decided to post about it, to get it out there to the Google Hivemind and Internet in case anyone else has the same problem as me.
Every now and then, I schedule posts on this blog to go live at a future date because it's convenient. But then they don't publish. Which is quite inconvenient.
After much hair pulling, searching, and a long conversation with my hosting company, the culprit is the WP SUPER CACHE Plugin. Almost all WordPress installations have it, so I'm pretty sure this is a common problem.
If you find that your posts are NOT publishing when you schedule them to, go to the WP SUPER CACHE plugin settings and DELETE THE CACHE. Just hit the button DELETE CACHE. I promise it won't screw up your website.
Once the cache is cleared, go back to your post that didn't publish, and re-schedule it to go live in the next few minutes, then monitor to see if it works and publishes for when you wanted it to go live. The problem should be all cleared up.
It seems I have to do this at least once or twice per year, and if I have to, no doubt other people do too. Hope this helps!
PS) Random featured image up there because I don't have one made for WordPress issues. It was a bath bomb. Such cool colors!