Due to a known issue CONF-32174
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Getting issue details...STATUS, the page to rebuild the ancestor table is not accessible in Confluence 5.4.1 and later. You will need to apply the workaround described in the bug report to be able to access this functionality.
In Confluence, the ancestor table defines what pages are ancestors or descendants of other pages (which can be used by search restrictions with the ancestorids restriction). Occasionally, the ancestor table will become out of sync. When this happens, you can rebuild the table to restore everything to normal.
After rebuilding the ancestor table, you'll need to flush the "Inherited Content Permissions" cache in Cache Statistics, otherwise the inherited permissions may not be applied immediately to all pages. You may also need to rebuild the content index so that the permissions take effect in search results.