Go to https://hub.gke2.mybinder.org/user/jupyterlab-jupyterlab-demo-0570jy0h/lab/tree/demo and run the jupyter notebook called "main.ipynb". I've ran the only cell in it for several times and now its stuck.
You can see the corresponding task at https://demoapp.trains.allegro.ai/projects/98cdb5ace38946a690daec8efd668a76/experiments/db0088e1207440319d80acc3ac89aafb/execution?columns=selected&columns=type&columns=name&columns=tags&columns=status&columns=project.name&columns=users&columns=started&columns=last_update&columns=last_iteration&columns=parent.name&order=-last_update . There are now two tasks in a "Running" state, one of them is generated by another run that I've made in a terminal and terminated.