https://phabricator.wikimedia.org/dashboard/view/125/ was setup to be viewable by anyone, even without a Phabricator account but it didn't seem to be the case. For instance in an incognito mode I saw "Login or Register with LDAP"
After investigation, we discovered that the panels inside the dashboard were not set to public which cascaded to the overall board.
This is clumsy as adding a new panel can break the overall permissions of the dashboard and is not obvious to the user at all.
Upstream task: https://secure.phabricator.com/T8033