The problem is that when you’re in the footer that WP/ACF doesn’t know what post to get the field from. In this case you need to supply the post ID. This is covered in the get_field() documentation http://www.advancedcustomfields.com/resources/get_field/ and this is how you can do that
<?php
$queried_object = get_queried_object();
if( get_field('sub_footer_section', $queried_object->ID) ):
<section class="subfooter">
//with a few of:
the_field('field_name', 'options');
</section>
endif;
?>
