404 error after removing “category” from URL structure

I removed the “category” from URLs and it is working on the posts. See this link for an example of a post:

/processes/quenching/quenching-news/360-degree-part-design-listen-to-your-heat-treat-department/

However, if you remove the post name in this URL which would result in:

/processes/quenching/quenching-news/

we get a 404 page not found error.

BUT if I add “category” before the first directory folder, it works fine, like this:

/category/processes/quenching/quenching-news/

How do I make this URL: /processes/quenching/quenching-news/
show all of the posts in this category?

• This topic was modified 4 years, 10 months ago by Jan Dembowski. Reason: Moved to Fixing WordPress, this is not an Developing with WordPress topic

The page I need help with: [log in to see the link]