With my first WP installation I was able to access topics under nested categories (subcategories) with permalinks like:
http://mydomain.tld/category1/subcategory2
After upgrade, this does not work anymore. Valid URL is
http://mydomain.tld/category/category1/subcategory2
The original permalinks were stored in some serach engines and I see in logs attepts to access them
How can I fix this?