Symptoms

After upgrading to 4.6.10, the customer receives the error "Sequence contains more than one matching element" when trying to create new workflows or edit existing workflows.
 

Diagnoses

In the SmartObject Tester Tool -> SmartObject Explorer -> System -> SharePoint 2013 Integration -> SharePoint Integration Helper Methods -> Methods, the "GetDesignerData" method is missing.

The appdeployment.exe completed, but logged the error "Cannot validate argument on parameter 'AppPrincipal'. The argument is null. Supply a non-null argument and try the command again"
 

Resolution

In reviewing the ULS logs during the appdeployment.exe, we established that the error was a result of not using an account with the correct permissions during the deployment. We re-ran the appdeployment.exe as the service account, and it completed successfully, however the error persisted. We checked and the GetDesignerData method was still not added. The customer ran a repair on the K2 for SharePoint component, and the method was added. This also resolved the error.