Symptoms

K2 for SharePoint app configuration and even the K2 Worklist now coming up blank.
Today in production across multiple SharePoint K2 App enabled sites the K2 App is not functioning. Clicking on the K2 App brings up a blank screen. K2 Worklist shows up as blank. This was all working yesterday correctly. I tried adding the K2 App to a new site but the registration screen never comes up. Right now none of the K2 workflows are working because they can't see their tasks in SharePoint

The K2 Workspace is working fine. Restarted the K2 service and token service but that didn't help.

 

Diagnoses

During the meeting we checked and noticed that the issue occurred with all third party SharePoint apps not just K2.

 

Resolution 

The problem wasn't related to K2 but to a WFE that had the Request Management Service turned on but the other didn't. Disabling that SharePoint service resolved the app catalog problem.