I couldn’t auto-save or just regularly save any post on WordPress 5.0. A google search turned up a few options but none of them worked for me.

Suggestions included changing permalinks then changing it back. There was a php.ini line that I tried. I think if I would have reverted to the old editor it might have worked.

While troubleshooting I checked Google Debugging at it was showing access-control-allow-headers errors. I searched for that and came up with almost nothing except one little gem of wisdom. it said that the URL I was using might be different than that of my site. Specifically, the hits were talking about http vs https. My SSL was good so I didn’t think that was the issue.

What I did notice was my admin page was lacking the www even though the admin section (and nothing in wp-settings) was www. I changed my settings to remove the www and then everything worked.

Be forwarned this will probably affect your SEO. Google showed only “www” links but now I am getting rid of the “www”.