How to trace down to find where a field has been removed/hidden of a particular node
some things to look at: make sure under display, that the type of display is set correctly (full content, teaser, default, etc). Check if field permissions or similar is installed and that the permissions for that field are set correctly. Check for any rules or actions that could be causing it to be removed.

another - is it in a field collection, display settings for those are shown under /admin/structures/field collections not under the content type