Suddenly, I found out that a Thousands of errored and cancelled Workflow in myList.

I could not find a reson for that and the users keep receiving emails for those errors(workflow failed to run)

Actually we have the august Cumulative update in our farm, So we did this PS code to run all SP2010 Workflow:

Add-PSSnapin Microsoft.SharePoint.PowerShell
$farm=Get-SPFarm
$farm.EnablePreParseSecurityCheckForWorkflow = $false
$farm.update()

Also , I found this nintex article for the failed to run error  and we did the PS code also:

$webapp = Get-SPWebApplication -identity http://<web app name>

$webapp.UpdateWorkflowConfigurationSettings()

And we  purge nintex Workflow history List 

NWAdmin.exe –o PurgeHistoryListData -siteUrl http://yoursite.com/ -lastActivityBefore 2014-07-01 00:00 -state SELECT STATE‍‍‍‍‍‍‍‍‍‍‍‍‍‍

After All that ; i still have the problem.

Any help please, it's on PROD environment and its for thousands Workflow instance.

Thank you