On the All of US Workbench, users are logged out after 30 minutes of inactivity. For long running jobs, this means that users may not have all notebook cells populated even though the notebook continues to run to completion. If you wish to capture all notebook cell outputs, use this notebook to run your long-running notebook (or any other long-running notebook).
But also note that for your analysis the cluster will autopause after 24 hours. To prevent your cluster from shutting down if your background job takes longer than 24 hours, be sure to log in and start a notebook, any notebook, to reset the autopause timer.