button to go up

Hi.

First of all I want to apologize for my English, it is not very good.

I am experiencing a strange thing on my website.

40elefantes.com.es

I have the button that goes up to the top of the web, the one that is at the bottom right. For a while now when I press it the web goes up, but at a very slow speed. I could say it goes up pixel by pixel. This only happens on the home page, but nowhere else.

I've thought a lot about some recent change, but I don't know what may be happening.

Does anyone know the solution or has this ever happened to you?

Thank you