Similar here. The custom fields would appear when I started a new post, but once it was saved as draft or published, the fields disappeared. The content appeared on the published page, but no longer editable, because it just wouldn’t appear in the edit screen. This was also happening with all the old posts–the content was visible on the finished page, but not in the edit screen.
This only started happening when I updated the ACF plugin last Wednesday to 5.7.7. I upgraded to PRO, and now everything is back to normal, so I’d say there’s definitely a bug in 5.7.7.
