Microsoft Entra ID (Azure AD) OAuth2 only works on the very first login. Subsequent logins authenticate successfully on the Entra side but redirect to the client home page without logging the user in.

This appears to be a Guest User session issue. Clearing all browser cookies/cache/sessions may temporarily resolve it. The session patch referenced at https://forum.osticket.com/d/107272-authentication-required-error/2 may or may not help depending on direction -- try reverting it if applied. If the only fix is deleting the user account, there may be duplicate or conflicting user records in the database that are causing the match to fail on subsequent logins. Debug the authentication pipeline in index.php and ticket.php to identify where the session or user lookup is failing.