I was prototyping some code around Session management in Jenkins with standard Jetty's HashSessionManager. This session manager tries to serialize sessions and their attributes to the disk. In Jetty all session attributes are supposed to be serializable, especially if they declare the Serializable interface.

In SSE Plugin EventDispather instances cannot be really serialized, because classes like PubSubBus and Authentication instances are not serializable in Jenkins core it causes failures in Session management.