Hey Tiago,
the portfolio doesn’t scroll up after applying a filter because I didn’t envisage that the one-page template would be used with a lot of portfolio items :) my bad. Anyways, I’ve prepared an improved piece of code: please download this archive, unzip it, and upload the contained file into the theme folder (/wp-content/themes/Kanso/). Then refresh the website and test the filter once more – let me know if it is working better now!
Sincerely,
Andrii / Satori Studio