I've added the Article button at the bottom of the editor, which is a Joomla Core button for adding links to articles. If you use this to create the Next link, it creates an almost idential link (same id and catid but omits the alias values), which gives exactly the same 404 result when clicked.
Just because you're not paranoid doesn't mean everybody isn't out to get you.
That's not a good option as I'll have 6 submenus on my site.
These articles have been on my website for over 5 years. It's only when I went into it to change some text they stopped working. I've had quite a few gremlins like this since I upgraded to JCE Pro. Joomla should or did use to allow direct link to article content.
I'll probably just create a page break and condense the 6 articles I have into 1.
I've got quite a big site with lots of articles. I'm concerned it'll be broken elsewhere that I don't know about.