Children Macro that contains lots of children's does not load for non admin user

Issue Summary

Children Macro does not load for non-admin users(i.e users which are not member of Confluence administrator group) which contains lot of child pages.

Steps to Reproduce

1. Use this space export to load a sample page(B2B matrix platforms - 1625644428754) that contains a lot of childrens(6K or above) and uses Children Macro under 7.12.2.
2. Children Macro configured above has "Show Descendants" option checked.
3. Try to log in as a normal user and you would experience an error "'page: B2B matrix platforms - 1625644428754 v.3 (327704)' exceeded the timeout of 120 seconds by -120000 milliseconds"
4. Login as an admin user and the page loads fine within few secs.

Tested under 7.8.3 and this works fine for both admin and non-admin users and hence creating a new bug to track this apart from CONFSERVER-43191

Expected Results

Page should load fine for a non-admin user as well.

Actual Results

Page does not renders and time out.

The below exception is thrown in the atlassian-confluence.log file post adding package content.render.xhtml.DefaultRenderer to DEBUG

2021-07-19 13:10:33,607 WARN [http-nio-8090-exec-6] [render.xhtml.transformers.DefaultFragmentTransformer] transformFragment Rendering: 'page: B2B matrix platforms - 1625644428754 v.3 (327704)' exceeded the timeout of 120 seconds by -120000 milliseconds
 -- url: /display/TEST/B2B+matrix+platforms+-+1625644428754 | page: 327704 | traceId: bf7cdc0d125eb9b1 | userName: saurabh | referer: http://localhost:8090/index.action | action: viewpage
2021-07-19 13:10:33,608 ERROR [http-nio-8090-exec-6] [content.render.xhtml.DefaultRenderer] renderWithoutMetrics Rendering this content exceeded the timeout of 120 seconds.
 -- url: /display/TEST/B2B+matrix+platforms+-+1625644428754 | page: 327704 | traceId: bf7cdc0d125eb9b1 | userName: saurabh | referer: http://localhost:8090/index.action | action: viewpage
2021-07-19 13:10:33,609 DEBUG [http-nio-8090-exec-6] [content.render.xhtml.DefaultRenderer] renderWithoutMetrics The content that could not be rendered:

Workaround

Uncheck "Show Descendants" check box and this works fine for a non admin user as well.