I've deactivated all the plug-in installed: Advanced Custom Fields, Disqus Comment System, Flexible Custom Post Type, WPML Multilingual CMS and WPML String Translation, refreshed the page multiple times, but the problem still the same. This is the url I call: site.com/category/page/2 does it points to archive.php or should I point to somewhere else? I'm not using other sub archives.

sorry for my english, i meant I've set the number of posts per archive by 1 by setting it in wp-admin > options > reading

I did it via wordpress backoffice wp-admin > options > reading

In archives I didn't set any number of posts, I just set it in reading setting, do you mean there is another place where I should set the number?

perfect! this is exactly what I was looking for.