Main menu dissapiar when selecting categories

Hello,

I’m using Hueman theme with WP latest version and something weird happens when I select a category to navigate; the main menu dissapear. Here are two examples of what I mean: http://www.euroviajar.com/blog/ and http://www.euroviajar.com/turismo-en-atenas/.

I need some help because I don’t know where to start looking for a solution.