Update the value of every page’s content editor with the value of an Advanced Custom Field on that page

Solution: Add this to functions.php and refresh admin once. Remove after.

function process_post() {
    $my_posts = get_posts( array('post_type' => 'page', 'posts_per_page' => -1 ) );
    foreach ( $my_posts as $my_post ) :
        $value = get_field('course_content', $my_post->ID );
        if($value):
            $update_post = array(
                'ID'           => $my_post->ID,
                'post_content' => $value
            );
            wp_update_post( $update_post );
        endif;
    endforeach;
}
add_action( 'init', 'process_post' );

 

I also noticed that some fields were visible to the backend but not rendering on the site. Perhaps some type of database cache. I fixed this by refreshing the field values with similar logic:

function process_post() {
    $my_posts = get_posts( array('post_type' => 'page', 'posts_per_page' => -1 ) );
    foreach ( $my_posts as $my_post ) :
        $value = get_field('field_560094b2af64e', $my_post->ID );
        if($value):
            update_field( 'field_560094b2af64e', $value, $my_post );
        endif;
    endforeach;
}
add_action( 'init', 'process_post' );