The author key/value query won’t work.
Try modifying the query by moving the query out of the meta query like so:
array(
'author' => $author,
'meta_query' => array(
'relation' => 'OR',
array(
'key' => 'leads_status',
'value' => '-1',
),
array(
'key' => 'leads_status',
'compare' => 'NOT EXISTS',
)
)
)