Just some guidance on where and when workflow history / Reporting should be avilable and from where you can access it.
Site Contents > K2 app > Reports – this is where you should go to see all of the workflows for all of the lists on a site. You can drill into the individual workflows and workflow instances via the UI.
List > Ribbon > K2 > Report – this is where you should go to see all of all workflows for a list. You can drill into the individual workflows and workflow instances via the UI.
List > Item > Context Menu > K2 Workflows – the design intention of this page is merely to allow you to Manually start a workflow for the currently selected SharePoint Item. The Workflow History section is a subset of the workflows accessible via Reports trimmed to only those instances for the currently selected Item. Furthermore, the instances are limited to only those workflows started via this page (Manual) or via a SharePoint event receiver. Workflows started directly via the API are not available via this view as it was never intended to be used for reporting.
Please view the proposed solution from the following URL; http://community.k2.com/t5/K2-blackpearl/Missing-Workflow-history-on-sharepoint-list-items/ta-p/9216... for the related problem.