Subscriber normally will re-register when it thinks it gets disconnected from statestore in its own perspective. So it will register again. And statestore will push a new update for the newly subscribed clients without cleaning previous already scheduled(queued) one.
If heart beat failed to catch up. those two queues will be filled full and may cause
IMPALA-2642 (this can lead to dead lock).
Essentially every new register will have one more update in queue. So we may end up with repeated scheduling for the same subscriber without notice.