The first kind of event, with keyspace prefix in the channel is called a Key-space notification, while the second, with the keyevent prefix, is called a Key-event notification.
Because Redis Pub/Sub is fire and forget currently there is no way to use this feature if you application demands reliable notification of events, that is, if your Pub/Sub client disconnects, and reconnects later, all the events delivered during the time the client was disconnected are lost.
The expired events are generated when a key is accessed and is found to be expired by one of the above systems, as a result there are no guarantees that the Redis server will be able to generate the expired event at the time the key time to live reaches the value of zero.