So, without changing any code on my end, I now get this message whenever I try to edit a page in Cornerstone. This happens on all pages, including when I add a new one, and in all browsers. It’s rather inconvenient, to put it mildly.
I also noticed that the X templates previously assigned to my pages seem to be missing when the pages are edited in the normal WP way; the only options are “Default Template” and a custom one that I have previously used. Where’d the templates go?