Sometimes GitHub has trouble rendering the notebooks. AFAIK the rendering system is behind the scenes at GitHub. Others have this same problem across repos and it sometimes occurs to me as well.
If the notebook won't render in GitHub, you can copy the URL to the notebook you want to view and use the following site to view the notebook: https://nbviewer.jupyter.org/
Sometimes GitHub has trouble rendering the notebooks. AFAIK the rendering system is behind the scenes at GitHub. Others have this same problem across repos and it sometimes occurs to me as well.
If the notebook won't render in GitHub, you can copy the URL to the notebook you want to view and use the following site to view the notebook: https://nbviewer.jupyter.org/