Symptoms

Domain group given specific access to a form, but are receiving "This page can't be displayed". After adding the runtime server IP to the user's host file, they now receive "The remote sever returned an error: (401) Unauthorized. Failed to initialize the Context".
 

Diagnoses

Users needed to have minimum Designer rights in the site collection in order to interact with K2 and SharePoint 2013 due to Microsoft Consent Framework. They had only been given participant permissions previously.
 

Resolution

Added the domain group to a SharePoint group which was given Designer rights on the K2 Permissions page.