The issue is that Boeing added a software layer to make the plane behave like the old 737, so pilots would be able to fly it without any extra training or addit

The issue is that Boeing added a software layer to make the plane behave like the old 737, so pilots would be able to fly it without any extra training or additional certifications. If it turns out that the pilots actually need some training to reliably fly the 737 MAX, there could be some nasty consequences for Boeing.