Sorry to be a pain again. I was trying to set my default layout to full width but keep the front page (home page) with a right sidebar. I know I can set the default in the customize menu area but it changes the front page and I cant find any option to set the front page by itself.
I have tested the shared child theme on my test site by setting WP debug on and it’s working fine without any issue.
Please make sure the following function activello_header_search_filter exists in the functions.php file of your parent activello theme and you are using latest version of it.
Turns out I didnt have the latest version. I was using 1.0.0, im so used to wordpress notifying me when there are updates for plugins etc that i didnt think to check your site for updates.