Why do I see extra service instance managers (SIMs) when the session manager (SSM) is recovering?

If an SSM crashes while its SIMs are in the middle of running tasks, those SIMs will try to gracefully shut down after they detect communication lost with the SSM. Those SIMs will wait up to the "Timeout duration" defined in the application profile's Service > Control > Method section for DestroyService (default 15 seconds) for the SI to clean up, before forcefully killing the SI and then exiting itself. Meanwhile, new SIMs may start up, replacing those that are shutting down.