I’ve looked at your code a couple of times now, and the only error I can see is in the query args, and I don’t think it would cause a problem.
$args = array(
'post_type' => 'pixie_testimonial',
'post_status' => 'publish',
// should be order
//'orderby' => 'ASC',
'order' => 'ASC',
'posts_per_page' => 999,
);