I'm loathe to go to species (or even genus) with these pentatomid immatures, as I don't know them. They could be Poecilometis, but Theseus is also an option (if it occurs here).
The suggestion was based on the following confirmed sightings of this species: Poecilometis strigatus (Gum Tree Shield Bug) on 5 Feb 2017 & Poecilometis strigatus (Gum Tree Shield Bug) on 15 Mar 2009 Perhaps we should review some of the sightings on the following species page in view of your doubts: https://canberra.naturemapr.org/Community/Species/Sightings/20119