When the workflow is throwing an error and detailed error is written in the Nintex Workflow History List, the user does not receive the email error notification even though it has been set to receive the Nintex Workflow Error notificaiton
From the log file we can find this entry:
Nintex.Workflow.NWNotificationException: From or reply to address settings not found. Make sure that the settings in the central configuration are correct
1) Navigate to Central Admin > Nintex Workflow Administration (2013) or Nintex Administration (2016, 2019) > Messaging and Notification
2) Verify that the From Address and Reply-To address is not empty.