FWIW, when you use a taxonomy.php template, it will be used for all taxonomy requests except when there is a more specific template like category.php. Perhaps for your site that arrangement is fine. If you did need to have your template apply to only your specific taxonomy, name the template taxonomy-{$tax-slug}.php where you replace {$tax-slug} with your actual taxonomy name or slug.
You should not need to create a new query for this. The original main issue query should work for your needs. By default the posts are listed in the wrong order, but that can be corrected easily. Creating a new query to replace the original is wasteful since you force WP to get all the proper issues from the DB, only to be ignored and asked to get the issues all over again in a different order.
Maybe that makes little difference now. On very large DBs and/or heavily trafficked sites it will make a difference. To do this properly, you need a template that just runs the standard Loop, no queries for content are needed. Probably like the archive.php template that is part of your theme. If your taxonomy.php has some other useful content you want to retain, you would need to remove the custom query and convert your loop to the standard WP Loop. Things like $cat_posts->have_posts() become just have_posts(), etc.
Another advantage of correcting the main query is pagination, if needed, will work without any problems.
To correct the order of posts, we hook the “pre_get_posts” action. We confirm the query is indeed one that we want to alter. If so, we simply set the ‘order’ query var to be ASC. If there were anything else to correct, it can be done here as well. I believe all the defaults will meet your needs, so setting that one query var should do it. The following code would go on your theme’s (preferably child theme's) functions.php.
add_action('pre_get_posts', 'fix_nummer_order');
function fix_nummer_order( $query ) {
if ( $query->is_main_query() && '' != $query->get('nummer')) {
$query->set('order', 'ASC');
}
return;
}
Untested. Let me know if you have any difficulty. I’m assuming your taxonomy name or slug is “nummer”, if not adjust the code accordingly.
