Have you tried just getting the “location” field when looping through the “Producers”?
<h4>Transaction Contacts</h4>
<?php
$producers = get_field('transaction_contacts');
if($producers):
?>
<ul class="list-unstyled">
<?php foreach( $producers as $p) : ?>
<?php
$office_location = get_field('office_locations', $p->ID);
?>
<li>
<p><?php echo get_the_title($p->ID); ?></p>
<?php foreach( $office_location as $o) : ?>
<p><?php echo get_the_title($o->ID); ?></p>
<?php endforeach; ?>
</li>
<?php endforeach; ?>
</ul>
<?php endif; ?>
