[Resuelto] Menu Language Switcher - Cannot select menu or Save it

Background of the issue:
I am trying to: I am not able to select any menu under Menu Language Switcher or Save anything there. It started about 4-5 months ago. I tried everything from disabling all plugins, switching the theme, but nothing help at all. I used to have the menu language switcher in the menu bar for many years, but after a WordPress or WPML it disappear and it is not working anymore. Can you help me to get it back? Link to a page where the issue can be seen: enlace oculto

Symptoms:
Cannot select menu or save it under Menu Language Switcher.

Questions:
Why can't I select any menu under Menu Language Switcher?
Why can't I save anything under Menu Language Switcher?
What could have caused the Menu Language Switcher to disappear after a WordPress or WPML update?
How can I get the Menu Language Switcher back?