QAbstractItemModel data() is NEVER called

The problem is this fragment:

int ModelItemNeural::rowCount(const QModelIndex& parent) const
{
    if (parent.isValid() == false)
    {
        return 0;
    }

You're basically saying that the root node (indicated by invalid parent index) has zero children i.e. the model has zero top-level rows. So the view queries no further.

Just drop this check and it should work. nodeFromIndex seems to handle root node correctly.