Order by two meta values – one is a number and the other is text

by

If the atsc_bod_listing_order meta is a number, then you should set the type argument to NUMERIC like so, so that the meta value is casted as a number which then gives you the correct numerical sorting:

'listing_order' => array(
    'key'     => 'atsc_bod_listing_order',
    'compare' => 'EXISTS',
    'type'    => 'NUMERIC',
),