Same problem here. The app seems to run python on remote server and it won’t display any output if it can’t connect.
Managed to solved the problem by forcing upgrade of jupyter notebook to 5.3.1
Warning: I don’t know of this will break anything in the virtual env
conda install notebook=5.3.1
pip install notebook==5.3.1
pip3 uninstall tornado
pip3 install tornado==5.1.1