Symptoms

We "Appified" a SharePoint 2013 library and went into the designer. We created sub-categories and moved the views, forms, smartobjects, reports and workflows into those sub-categories. After the move, we no longer see the K2 artifacts when we click the "Application" button on the SharePoint 2013 ribbon menu. (This worked in 4.6.10)
 

Diagnoses

In 4.6.10 we iterated through all the sub-categories of the selected folder and showed you all the K2 artifacts in the current category and all sub-categories. When your structure becomes larger, it takes time to loop through all the sub-categories and this became a performance bottleneck. Due to this bottle-neck, it was decided to remove this feature to iterate through all the sub-categories (For performance reasons).
 

Resolution

This is the "new norm" and what we saw is expected results for 4.6.11 (And onwards.) This was done to improve overall load performance in the K2Designer.

The official "fix", is to move the K2 artifacts back into the "main/parent" category. This will display the K2 artifacts in SharePoint when you click the "Application" button again.