For security purposes, if you are inactive within the Researcher Workbench for 30 minutes you will be automatically logged out of the system. If you have long-running Jupyter Notebooks with active or pending cells, they will continue to execute after you have logged out. However, without an active user session, output cells and execution history will not be saved to the notebook. To avoid losing work in this situation, update your notebook code to write intermediate/final outputs to local files (temporary) or to your workspace's Google Cloud Storage (GCS) bucket.
To check if you have a running runtime ("cloud instance"), click the "Compute Configuration" icon on the sidebar of your workspace. A green dot will indicate if it is running, a yellow dot if it is paused, red dot if it is stopped, and nothing if the runtime is deleted.
To learn more about how to do this, view this video here.