Getting correlation ID when clicking the link "Click here to show detailed view" in the workflow history screen (should redirect to workflowlog.aspx)
Logs return:
System.Data.SqlClient.SqlException: Timeout expired. The timeout period elapsed prior to completion of the operation or the server is not responding.
Anyone any ideas why this might happen?
Workflow-History List or corresponding database tables too big?
Did you make sure the sql server is working properly? Are other operations working as expected?
Did this continue to occur? Even with a large database, this shouldn't be a major query because they are indexed. I'm wondering if the server just couldn't respond in the SQL default 60 sec timeout.
Sounds like you need to speak to your Farm Admin 
Nintex support have also sent me to this page for troubleshooting - will let you know how it works out 
thanks
Andrew Glasser Nintex support have asked for this:
Could you please send us the result of this few things below.
1. Disk Usage Tables.
2. Nintex Workflow History list item
So I will let you know how we get on with that.
There must be regular maintenance in place for the database, such as statistics updates, index rebuilds, etc.
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