Scenario: Session Prelaunch is configured for all users in an environment. A new user complains about slow logon. A Citrix Administrator finds that Session Prelaunch is NOT working as expected for the

HTML5 Receiver does not support Session Prelaunch, but the symptom here is that prelaunch is failing rather than being unsupported, and the question does not indicate the user is on HTML5 Receiver.

The NetScaler Gateway plug-in is required for remote/VPN access scenarios but is not a dependency for Session Prelaunch functioning on an internal network.

The /includeSSON switch during Citrix Receiver installation enables the Single Sign-On component, which Session Prelaunch depends on to silently authenticate and start a session in the background before logon completes. Without this switch, the SSON component is absent on that endpoint, so the prelaunch session cannot be authenticated, causing the slow logon the user experiences. Because all other users have Receiver installed correctly, only the new user - whose Receiver lacks /includeSSON - is affected.

A missing user certificate would cause authentication failures at a certificate validation stage, not specifically break Session Prelaunch while leaving all other users unaffected.