Symptoms

When actioning a workflow step from the browser, after following the link to the item display form, we are getting the error: "2640 Worklist item serial number here] not found for AAD::username here] at 127.0.0.1:38024.
 

Diagnoses

What is strange is that the workflow step actually happens and we have not seen this error until yesterday afternoon. We have a similar step in the same workflow that works without this pop up error.
 

Resolution

Issue: Worklist item not found error on User Task submission.

Resolution: The User Task was set to use a workflow-generated state on its associated form but the workflow generated its task rule in the base state. Removing the custom state and changing the User Task's associated state to the base state solved the issue. Alternatively, if one wanted to retain their custom state, deleting the rule from the base state, verifying the workflow User Task wizard rule-injection step is correctly configured, and redeploying the workflow should re-inject the workflow rule into the correct state.