I cant say what exact version this crept in, but if you specify a shadowLight.shadowMaxZ value, the shadow does NOT render at all. Any value. But if it is left undefined it renders fine but you can no longer set the desired max shadow distance for your real time shadows.
Its hard to reproduce on the playground. Because of the architecture of the playground its hard to create a shader generator within the default createScene. You get an error talking about the scene has to be created first. Probably would be better to pass the scene object in the ShadowGenerator constructor just like any other babylon entity that required the scene.
But none the less. Any value on shadowLight.shadowMaxZ causes shadow to not render