It seems like the full width setup is changing the header layout? I tried using the Header Search component, but it doesn’t show with the theme.
edit: ok, that’s weird. The component didn’t show on my instance where it was already installed and I added the theme. But when I install it after the theme, it shows.
Also, the sidebar scrolls up along with the composer. Well, it also does that on the default layout. But it looks a bit strange when the sidebar is not above the composer, but left of it: