Search results sort order failing: set by date only

Question

Hi the default wordpress search seems to be for "piano"

SELECT SQL_CALC_FOUND_ROWS wp_posts.ID
FROM wp_posts
WHERE 1=1
AND (((wp_posts.post_title LIKE '%piano%')
OR (wp_posts.post_excerpt LIKE '%piano%')
OR (wp_posts.post_content LIKE '%piano%')))
AND wp_posts.post_type IN ('post', 'page', 'attachment')
AND (wp_posts.post_status = 'publish'
OR wp_posts.post_author = 5
AND wp_posts.post_status = 'private')
ORDER BY wp_posts.post_title LIKE '%piano%' DESC, wp_posts.post_date DESC
LIMIT 0, 25

however I need them all sorted by date first. My search results by date are skewed:

2020-10-25  
2020-10-22  
2020-10-20  
2020-10-20  
2020-10-16  
2020-10-13  
2020-10-10  
2020-10-07  
2020-10-06  
2020-10-02  
2020-09-30  
2020-09-28  
2020-09-02  
2020-08-09  
2020-07-21  
2020-07-21  
2020-05-21  
2020-04-24  
2020-03-06  
2019-06-02  <- here it is skewed onwards
2019-06-01  
2020-10-25  
2020-10-24  
2020-10-23  
2020-10-23

So I asume it is because the SQL query sorts by title first.

So I tried this solution:

function changeSearchSort( $orderby, $query ){
    global $wpdb;

    if(!is_admin() && is_search()) {
        $orderby =  $wpdb->prefix."posts.post_date ASC";
    }
    return  $orderby;
}
add_filter('posts_orderby','changeSearchSort',10,2);

from here How do I change WP search results order?

and it does not work.

I have tried this:
a) disabled all plugins
b) different themes

still not working.

Help appreciated

cheers

Ben