Symptoms

The user has a workflow that errors when it reaches the step that executes the Restore Version Documents wizard. The error it throws is as follows: Message: The attempted operation is prohibited because it exceeds the list view threshold enforced by an administrator.
 

Diagnoses

While this is a legit error exception that's getting bubbled down from SharePoint (K2 leverages the SP CSOM API for executing the 'Restore a previous version' functionality at runtime) due to the size of items in the document library i.e. over 9K items, we were able to negate the issue by doing a re-design of the 'Restore to Previous Version' event in the K2 Designer wizard . The redesign involved adding a new method to the underlying SmartObject definition that retrieved the document items using the ID in lieu of the document name.
 

Resolution

An isolated fix was provided to customer in the form of a patch. The FIX itself will be pushed into the product when Appit 1.5 Update 2 ships sometime mid-January 2017. If you run into a similar issue post Appit 1.5 Update 2 please contact K2 Support.