Hi @almazka
I think it’s because your posts_where hook modified ACF’s fields (which is also a post apparently). I believe you need to check if the queried post is not acf-field like this:
add_filter( 'posts_where' , 'my_where', 10, 2 );
function my_where( $where, $query ){
global $wpdb,$wp_query;
if ($query->query_vars['post_type'] != 'acf-field') {
$where .= " AND wp_posts.post_title LIKE 'b%'";
}
return $where;
}
Hope this helps.