Upfront theme with fixer as a child

I have a lot of problems with the posts element.

a. I was able to add 6 posts in the main page, but I can't use the next/prev pages. It's not loading. (see somosmascuba.net/v3)

b. I added in the menu a dropdown menu with categories (posts categories). Upfront was able to find those posts, but it's impossible to edit that page. Simply is not coming up in the upfront editor.

I granted access to the site.