In JIRA Service Desk 3.1.x, the Help Center was re-designed.
Search smarter on the global Help Center
We've redesigned the Help Center to focus on what matters most to customers. Customers can now use the global Help Center to view popular service desks, and search for request types and knowledge base articles across all service desks they have access to. This means customers no longer have to remember whether they need to submit a request for a new laptop in the IT Service Desk or Purchasing Service Desk. Simply searching for "new laptop" will display the correct request type automatically.
The improved smart search algorithm learns from past requests, so if customers have previously raised hardware requests for a laptop and monitor, they can search for "laptop" or "monitor" in the future to find the hardware request type. As your customers create more requests, the search algorithm gets smarter!
See: Release Notes
However, it would be nice to have the option to revert to the older style Help Center prior to this change.