And anyone here can only guess.
What is see is someone messed up big time by putting that slab so high.
It's a guaranteed way to end up with water inside the house.
It never should have been pored to within 4" of the threshold.
If they messed up on that then I'm sure the prep work was not done under that slab.
To me it looks like someone tryed to tie the slab into the slab on the house with rebar to connect the two. That's why when the slab lifted it took out the slab on the house.
Big no no, there should have been an expantion strip to sepperat the two.
When the outside edges fail it's a sure sign they did not dig a berm so the slab would be thicker on the edges.
Unless someone removed the tiles to see what's going on under it there only going to be able to guess.
Is the slab graded wrong and it's acting like a funnel poring water under the house slab?
Is the plumbing run through the slab, it's leaking and forming a void under the slab.
Is water getting in under the tile from the water leaking in under the threshold?
There needs to be gutters over this deck area at the least.