Umbraco CMS logout page displayed before session expiration

Umbraco, a free and open source .NET content management system, has an insufficient session expiration issue in versions on the 13.x branch prior to 13.5.2, 10.x prior to 10.8.7, and 8.x prior to 8.18.15. The Backoffice displays the logout page with a session timeout message before the server session has fully expired, causing users to believe they have been logged out approximately 30 seconds before they actually are. Versions 13.5.2, 10.8,7, and 8.18.15 contain a patch for the issue.