Resolution: Tracked Elsewhere
I've created a release note which I want to be publicly accessible. I've switched on Anonymous access, and then given anonymous users access to view the pages within my 'release notes' space.
Now, I can open my release note in a browser where I'm not logged in and can see it. Success!
BUT, if I'm logged in as a Service Desk customer, visiting the same link gives me a 'Not permitted' page. Surely customers should be able to view this page?
Atlassian Answers post here: https://answers.atlassian.com/questions/37547733/comments/37547778