This seems to be a bug. I’m trying to change the number of posts per page on a custom post taxonomy archive using pre_get_posts. In the function astra_blog_post_per_page() that is located in inc/blog/blog.php there is a way to provide exclusions using astra_blog_post_per_page_exclusions filter. However it doesn’t work because $query->get( ‘post_type’ ) doesn’t see the custom post type at this point.