The "Knowledge Breadcrumbs" widget is the OOB, however when pressing the "Knowledge" link from the breadcrumbs, it navigates to the index page. Note the URL displayed in the browser is:
However, the navigation works correctly for the /kb portal.
The KB Home Page was not set in the portal configuration.
1. Go to Service Portal >> Portals. Edit your portal.
2. Set the value for the KB Home Page to kb_view2 or any other page you would like to redirect. By default, the value is kb_view2 in latest versions.
NOTE: The /kb portal does not need this value since the homepage for this portal is kb_home.