Related listings not working correctly: use primary category

Related listings not working correctly: It should show other listings that are in the same category. But what if a listing is in more than 1 category? Then the related listings should be filtered according to the PRIMARY (main) category of a listing

Here I have 2 listings that are in 2 categories and both have the same primary category “Küchenabdeckungen”. But in detail view the related listings show other listings from the other parent category “Küchen”.
https://www.offerten24.ch/projekte/kategorie/kuechenabdeckungen/

https://www.offerten24.ch/projekte/aargau/murgenthal/kuechenabdeckungen/robuste-kuechenabdeckung-aus-glas/

And here there are no related listings at all. Why?
https://www.offerten24.ch/projekte/bern/seeberg/kuechenabdeckungen/swissculinaria-glasloesung-fuer-die-kueche/

“Küchen” is the Parent category of “Kücheneinrichtungen”. But “Kücheneinrichtungen” is the primary category of these 2 listings, so they should be related to each other.

Please use PRIMARY category for showing related listings, not any category of a listing.

My shortcode:

[gd_listings title=”Other Projects” post_type=”gd_project” event_type=”all” related_to=”category” sort_by=”latest” title_tag=”h3″ layout=”gridview_onehalf” post_limit=”4″ hide_if_empty=”1″ category=”0″]