Service Desk customers can't access public Confluence pages.
- Create an user with access 'Restricted Portal';
- Create a space in Confluence;
- Set Anonymous access on the space (Space tools);
- Try accessing the homepage of the space (created on step 3) using the user 'Restricted Portal' (created on step 2);
The user with 'Restricted Portal' should see the page assuming that it is open for all kind of users.
If the user opens the space using a incognito window, the pages is shown.
I reproduced the steps to create the issue in a Dog Food instance and the same error occurred.