Unresponsive Python notebooks or cancelled commands could be the cause of "Fatal error: The Python kernel is unresponsive." This can be caused by a number of problems, such as metastore connectivity issues or conflicting libraries.  To troubleshoot this issue, you can check for metastore connectivity and review the Cluster cancels Python command execution due to library conflict KB article for more information:

https://kb.databricks.com/python-command-cancelled