list_local_sessions.js will create a session and then will use $listLocalSessions to retrieve all sessions and the current user's sessions and verify that the created session is present.

The logical session cache will return these sessions from its _activeSessions. However, during a cache refresh (which happens periodically), these sessions will be temporarily swapped out until the backswapper goes out of scope. It is therefore possible for the $listLocalSessions command to fail to return the created session if the request is processed during this period of time when _activeSessions has been swapped.