Unable to view public Confluence pages while authenticated as JSM portal-only customer account

Issue Summary

When a user is authenticated under a portal-only customer account for a JSM portal (unlicensed user), they are unable to access any Confluence content that is open for Anonymous Users (Public) on the site.

Symptoms are a missing top-bar menu and pages will either present a "We can't find the page" message or pages load partially while displaying multiple error messages.

Steps to Reproduce

1. Create a JSM project. 
2. Add a new Customer using any email not linked to an existing Atlassian Account. 
3. In Confluence, go to the space used as Knowledge Base for this project and open it to Anonymous Users. 
4. Open a browser new session and log in to JSM Customer Portal.
5. Try to access any Confluence page/URL from the same site.

Expected Results

The page will load normally.

Actual Results

The page doesn't load - either presents a "We can't find the page" message or pages load partially while displaying multiple error messages. The whole site behaves inconsistently.

Workaround

• Logout of portal-only accounts and access the pages again (those that are open to the public - anonymous)
• Or open a new incognito/in-private window and access the open to the public pages (as long they don't log in)