Symptoms
Not able to use K2 app
We are not getting K2 component options in SharePoint List Ribbon
Diagnoses
The K2 for SharePoint app was previously on the SharePoint list ribbon and worked fine.
Resolution
This was resolved by doing the following.
On the affected site collection (or subsite), visit the site contents and remove (do not uninstall) the K2 Appit for SharePoint app from the site collection and re-add the app.
This resolved the issue with the K2 controls not appearing in the ribbon.