Track database name in anemometer queries
(Until I get answers to my comment, here is all I can suggest...)

1. LEFT and the two tests on wp_postmeta have no impact on the outcome; get rid of them.


Get rid of wp_postmeta all together.  And get rid of the GROUP BY, which was probably a byproduct of the JOIN.
INDEX(post_type, post_status, post_date)


That leaves you with just

select  *
    from  wp_posts
    where  post_type = ?
      and  post_status = ?
    order by  post_date desc 


Does that give you the right answer?