@killyourfm maybe try it again and see if maybe it'd have populated a list of updates if left to it's own devices.
Like, maybe package-kit was just still working on it. Gnome-software should have shown all those updates, unless zorin really broke something badly that is.
I don't use Zorin, but if they use the same gnome stack as Fedora (and a custody search suggests that they do) I suspect it was just still working on it.