I can recreate this same issue where if I click to “Update” a page it does not save. It’s a long shot but I have 100% narrowed it down to this plugin causing the issue for me: Pagely MultiEdit.
The issue occurred on a client site and on a clean test instance of WP I setup. If ACF + MultiEdit is active, then the page no longer saves. The issue is reported here: https://wordpress.org/support/topic/content-disappearing-from-tabs?replies=7
If either ACF or MultiEdit is deactivated then the pages saves fine. Hope this might be the issue for folks!
