Help on margin or padding issue

Hi,

I am making a site for a friend and I don't understand why some pages and posts have margin or padding (I still don't understand how to distinguish sometimes) before the footer and others don't.

I've made a 50 s video showing this. I think it will be better to understand if you could see it, please:

http://somup.com/cYhw0MjR7n

I started this site importing abstract from site library.

The pages that don't have that padding/footer before the footer are:

https://duorubrum.com/sobre-nos/

https://duorubrum.com/contactos/

What can I do to have the padding/margin?

Why some have and some don't?

Thanks in advance,
Ricardo Pons

P.S.: I'm new to GP and I'm loving it :)