FindOnBoard.jspa?sprintId link is extremely slow and fails to load

Issue Summary

Post upgrade to Jira 9, /secure/FindOnBoard.jspa link is extremely slow and fails to load,

i.e after clicking the link present in "Completed sprints" from "edit issue" section, it navigates to  to /secure/FindOnBoard.jspa?sprintId

e.g: https://jiraserver.test.com/jira/secure/FindOnBoard.jspa?sprintId=132345

This is extremely slow ~ 2.3 minutes and fails to load afterwards.

This is reproducible on Data Center: (yes)

Steps to Reproduce

1. Open a Jira issue associated with completed Sprints
2. Click on the "Edit" button (the "Edit Issue" dialog should open)
3. In the "Edit Issue" dialog, scroll down to "Completed sprints"
4. Click on any of the sprints listed there (either directly or to open in new tab)
5. Jira stays stuck loading forever 

Note:

• Number of boards ~28k
• Number of Sprints ~203828{}

Expected Results

Loading of board should load faster and successful 

Actual Results

Loading of board is stuck and it results client timeout.

Workaround

1. Increase AJAX calls timeout
   • See https://confluence.atlassian.com/jirakb/how-to-change-the-default-ajax-timeout-in-jira-824345485.html
   • This will work only for middle-sized instances. Suggested new timeout value: 120 secs
2. If possible, reduce the number of boards and their complexity:
   • Check scrum boards. Check the sprint dates for the current/last sprint. If a project is inactive then it is highly likely that sprints have not been planned in the recent few months.
   • Check kanban board. Run the created/resolved chart for the filter/project in that Kanban board and see. Again, if the project is inactive then not many new issues would had been created in recent past.
   • Check empty JQL board.
   • The list of JQL filters associated with all Boards can be retrieved running the below query:

     select rv."ID", rv."NAME", sr.reqcontent from searchrequest sr, "AO_60DB71_RAPIDVIEW" rv where rv."SAVED_FILTER_ID" = sr.id;
     

1. Disable the View on board functionality:
   • Block calls to /secure/FindOnBoard.jspa at proxy level
   • please see example for Apache Httpd:

     RewriteEngine On
     RewriteRule ^/secure/FindOnBoard.jspa - [F]
     

   • for nginx

       # Blocked FindOnBoard because of severe performance impact. Links
       # are not supposed to be accessible but people seem to keep find them.
       location = /secure/FindOnBoard.jspa {
         error_page 403 /403-page-disabled.html;
         return 403;
       }