Try adding artist ID as the second parameter in the_field(), like so:
<?php the_field('artist_summary', $artist->ID); ?>
http://www.advancedcustomfields.com/resources/functions/the_field/
Try adding artist ID as the second parameter in the_field(), like so:
<?php the_field('artist_summary', $artist->ID); ?>
http://www.advancedcustomfields.com/resources/functions/the_field/