I had to add [‘id’] to the end of get_field in order to get it to work.
<?php
$profile_pic = wp_get_attachment_image_src(get_field('profile_pic')['id'], 'profile-thumb');
?>
<img src="<?php echo $profile_pic[0]; ?>" />
get_field seems to return an array and not the id.
Thanks for this AMAZING plugin btw!