Hey – I don’t have a way right now to use filter when you have only certain categories listed in a page. May be you don’t need a filter when the portfolio items belong to a category and it’s children only. Here is the discussion of the shortcode you should be using to display portfolio items belonging to a one or more categories –
https://www.livemeshthemes.com/support/forums/topic/getting-portfolio-with-slugs/
Hope that helps. Thanks