"Non-retryable error executing action: 'gmail/get' cloud.solutions.Common.NonRetryableException
A task was canceled."
This is a temporary item-based error which occurs when exporting items from Google. It's literally a "Non Retryable Exception". It can occur during the migration of any G Suite services such as Gmail or Calendar, but the same solution applies to both.
Remigrate the user, it should reduce the occurrence of the error or resolve it completely.