Living wind, it looks like you had bare soil that you at least loosened up before putting down the sheet mulch. That could help enormously so the roots can penetrate deeper.
On my own side, I think 2 faults are, number one using wood chips in the sheet mulch, which, don't break down all nicely it seems, and number two, I have a strange feeling that the
compost I was using had some kind of chemical residue.
I just wanted to say that sheet mulch is not the be-all end-all awesome approach that its hyped up to be; using "any kind of organic matter" you have on hand doesn't always work, and you could probably still benefit alot from a onetime tillage before doing it.