Part 4 - 5.13.1.1 contains the following part:

"Subscriptions have a lifetime counter that counts the number of consecutive publishing cycles in which there have been no Publish requests available to send a Publish response for the Subscription. Any Service call that uses the SubscriptionId or the processing of a Publish response resets the lifetime counter of this Subscription. When this counter reaches the value calculated for the lifetime of a Subscription based on the MaxKeepAliveCount parameter in the CreateSubscription Service (5.13.2), the Subscription is closed. Closing the Subscription causes its MonitoredItems to be deleted."

I think instead of MaxKeepAliveCount parameter, LifetimeCount parameter should be used instead.