That’s weird. If you put it inside The Loop, the returned value should be right. Did you add the code in an included file? If that’s the case, then you need to get the global $post variable first like this:
$post_object = get_field('instructor', $post->ID);
If that’s not the case, then could you please share the full template code you have? You can copy a long code to https://gist.github.com/.
Welcome to the Advanced Custom Fields community forum.
Browse through ideas, snippets of code, questions and answers between fellow ACF users