The default settings for the multicast configurations you create are aimed at providing the lowest possible latency. With this in mind, the configuration is such that the multicast client will ack every one second, and the server will maintain a list of un-acked events (default 9000). If the publish rate exceeds 9000 per second, the delivery rates might be quite irregular. This is due to the fact that the client will only acknowledge every one second, and so the server will automatically back off the delivery until it receives an acknowledgement from the client and can therefore clear its unacknowledged queue. If this happens, you can change both the Unacked Window Size to be greater than 9000 and the Keep Alive Interval (ack interval) to be less than one second.