Hopefully someone can help because I am losing my mind over here.
So I have a custom field group and for some reason one of the fields is no longer showing up in the editor, the content still prints to the front end page but I can’t edit that field in the editor. All of the other fields in the group work fine.
I had a similar case, kept searching, and found this: https://support.advancedcustomfields.com/forums/topic/sync-option-not-available/
This comes definitely too late to the OP, but may help others landing on this thread.