Knowledge base articles can't be opened in some cases if Jira is connected to at least 2 Confluence instances

Issue Summary

When Jira is connected to 2 Confluence server instances via an application link, viewing a knowledge base article (KB article) from the request creation page might lead to either either below:

• Error 1:

  The knowledge base article could not be found.
  

  

• Error 2:

  We can't link to Confluence because of a problem with the metadata. You can try refreshing the page, but it probably won't fix this one
  

  

Note that opening the same KB article from the Customer Portal page (instead of the request creation page) will work properly:

This issue comes from the fact that:

• when the KB article is accessed from the portal, the KB URL contains the application ID matching the right Confluence instance, for example:

  http://localhost:8084/jira842/servicedesk/customer/kb/view/65606?applicationId=79df3f51-590a-36d2-9c2b-85f72a6b90d1&portalId=2&pageNumber=1&q=laptop&q_time=1578500997521
  

• when the KB article is accessed from the request creation page, the KB URL does not contain the application ID, therefore Jira selects by default the Confluence instance set as "Primary" in the application links page, rather than the one the Confluence instance the KB belongs to.

  http://localhost:8084/jira842/servicedesk/customer/kb/view/65606
  

Steps to reproduce

• Setup 2 Confluence instances
  • The first one will be referred to as "Confluence"
  • The second one will be referred to as "Confluence 2"
• Create a new space in "Confluence 2", and create a page containing the word "laptop"
• Setup 1 Jira instance
• Configure 2 application links in Jira, 1 to each Confluence instance, with the application link to "Confluence" set to the primary one:
  
• Create a Service Desk project in Jira, and configure there a knowledge base using the space coming from "Confluence 2"
  
• Go to the customer portal, select a request type, and start creating a new request
• From the request creation page, type "laptop" in the summary field. The KB search should suggest the KB page from "Confluence 2"
• Click on the KB article from the search result

Actual Results

The KB page is not open, and the following error is thrown:

The knowledge base article could not be found.

Note that if the "Confluence" instance is not reachable from Jira or not running, the following error will be thrown instead:

We can't link to Confluence because of a problem with the metadata. You can try refreshing the page, but it probably won't fix this one

Expected results

The KB page should open, as it's the case when we open it from the Customer Portal page (instead of the request creation page).

Workaround

Set the application link corresponding to the Confluence instance where the KB is coming from as "Primary".
In the event where both Confluence instances are providing KB functionality to Jira, the error occurs on the non-primary Confluence pages