Notebook stopped working. Cannot access and shows in notebook instances only intermittently.

It looks like the AWS IAM identity that you're logged in to the AWS Console with (going by your error message, the assumed Role voclabs) does not have permission to list SageMaker notebook instances.

If you use multiple Roles (or a combination of your own IAM User and assumed Roles), you may need to switch roles back to the identity you were previously using to access SageMaker.

If you always use the same role, it may be that the attached access policies have been changed (reference list of SageMaker IAM actions and resources here). You'll need sagemaker:ListNotebookInstances to list notebook instances in the console and sagemaker:CreatePresignedNotebookInstanceUrl to open Jupyter/JupyterLab on an instance. From the error message it looks like there's a permission policy attached to your role that's explicitly denying this access. Your administrator should be able to help with this, or can refer to the AWS IAM documentation and IAM service console if you manage the account yourself.