It may have already happened to you: some day you find out that you can no longer see the information of a workflow. That’s because SharePoint uses the Workflow Auto Cleanup Job to erase the completed workflow instances which their completion date is older than 60 days. Tasks are deleted too, so you may lose a lot of information. But there are ways to avoid this.
– If the requirement is to keep that information more time than 60 days, it’s possible to modify the workflowAssociation property “AutoCleanupDays” to increase the time that SharePoint should retain those items. But once that time expires, the tasks and the association will be erased.
– If the information should be always accessible, then the solution is to disable the Workflow Auto Cleanup Job. Those items will never automatically disappear. But keep in mind that the amount of information in SharePoint system will increase.
What if you have already lost information?
The hidden Workflow History list is storing the information you need. The task items are removed, and the workflow association has disappeared, but the History Workflow items still exists on the system. The hidden list is usually named “Workflow History” but if you can’t find it, I recommend you to use SharePoint Designer to find out its location. And when you open it you will see those items you thought you had definitely lost.