It is a bit worrying that the cracks are worsening, though. For instance we've had 2-3 more floor tiles crack this year in the same area. I've messaged Insider and will see what he says and go from there.
Insider has lots of knowledge into soil but the most importante person to contact is Dominic Lopes he is fantstic and he teaches he been doing this for over 40 years. Id get himto redo a soil test and he checks test for everything he's a person to have on your side as he wrote part of the AS 2870 well respected at vcat.
You can also pm me i have lots of information you can use.
Regards.