WordPress Screwing Up ‘orderby’ => ‘meta_value_num’ in ‘pre_get_posts’

by

Use a meta_query and set type to NUMERIC–

$query->set('meta_query', array(
    array(
       'key' => '_ai_price_int',
       'value' => array(0, 4000),
       'compare' => 'BETWEEN',
       'type' => 'NUMERIC'
    )
));
$query->set('meta_key', '_ai_price_int');
$query->set('orderby', 'meta_value_num');