Hi.
I have my own theme and ACF Pro latest.
Whatever I do, I do not get it to work.
Single picture in author.php
http://safeontrack.com/author/adminellesot/
Lots in a page.
http://safeontrack.com/fotografer/
Lates I tried is ID and the cod is like this:
<?php
$id_bild = get_field('id_bild');
$size = 'full'; // (thumbnail, medium, large, full or custom size)
if( $id_bild ) {
echo wp_get_attachment_image( $id_bild, $size );
} ?>