I think I have an issue caused by products being in multiple groups. Altough I must admit I am not sure.
I added an _Additional Information group, and below that a Brands folder to attach brand information to each product.
Before I did this the product overview would show products and then click through the detail page such as https://mountainbikemuseum.net/bikes/century
But now it generates URLS like https://mountainbikemuseum.net/&groupid=GROUP164&productid=ITEM1 resulting in a 404
Even when I set the primary group on a product, the detail URL still does not work:
Maybe someone can shed some light on when Swift will render a URL with the &groupid structure instead of a "normal" direct url, and what I should do to fix this?