For a short period of time after restarting the SQL server, as part of planned maintenance or updating, workflows might fail.
Stop the Windows SharePoint Timer Service five minutes before restarting the server.
This is due to workflows being woken up by the SharePoint Timer service and attempting to access the Nintex or SharePoint Content Databases. Stopping the Windows SharePoint Timer Service will allow enough time for any running workflows to stop, and also prevent any paused workflows waking up and attempting to access the database. It will also stop other SharePoint scheduled jobs from having issues while the database is down.