Confluence Search doesn't work in spaces open to Anonymous Access while authenticated as JSM portal-only customer accounts

Issue Summary

While having an active JSM portal-only customer account session logged in, the Search, Quick Search & Search Macro in Confluence does not work, despite having Anonymous Access enabled for site/spaces.

While browsing Confluence, there's also no indicator the user is logged in to any account (as this is JSM only) and even the 'Sign In' icon is displayed on the screen (top-right corner).

According to CONFCLOUD-70656, Confluence Search does not work for 'Unlicensed users', but it's expected to work if Anonymous Access is enabled. 

As soon the user forces a logout for the JSM portal-only account (via https://<instance-url>/servicedesk/ > Logout) or access Confluence via an anonymous window, the searches work as expected.

Steps to Reproduce

1. Ensure the instance has both Confluence and JSM.
2. Create a Confluence space and make it available to Anonymous Access
3. Go to JSM and create a new customer account (Portal-only, not linked to an Atlassian Account)
4. Log in to this customer account (via https://<instance-url>/servicedesk/)
5. Access Confluence while logged to this customer account (https://<instance-url>/wiki)
6. Search for any word you know it's present in one of the Confluence spaces with has Anonymous Access enabled

Expected Results

Search results display pages under the spaces that have Anonymous Access enabled

Actual Results

Search returns a "We're having trouble getting your results" error

Workaround

User has to open an incognito window to access Confluence and search for target pages.
Alternatively, user can access "https://<instance-url>/servicedesk/" and logout from their portal-only account, making the search in Confluence to work again.