Search pop-up for Confluence KB/Solution on the Main Portal shows blank

Steps to Reproduce:

1. Create two dummy Service Desk.
2. Configure an Application Link to Confluence with 2-Legged OAuth Authentication (2LOA) between the applications.
3. Link one of the Service Desk project to a Confluence Space.
4. Create an article/page on the Space.
5. Log out and access the Main Portal as one of the Customer.
6. Search for a Solution with the space name or article name on the Main Portal.
7. Click on the drop down search result.

Expected Result:
It will shown the article content

Actual Result:
It will shown a blank pop-up window or an error message from the browser.

Notes:

• If we go inside the linked customer portal, the search pop-up will worked perfectly.
• On the testing, it will actually ask for login to Confluence, either in Main Portal or Customer Portal. This is related to linked issue below.
• On some time, in the Main Portal the pop-up will show the Confluence Login notification overtime even though it is already logged in.