PubNub creates a persistent always-on TCP socket connection. What you are seeing is the subscribe HTTP requests. Each request will be completed either when a message is published to the channel(s) that are part of the subscribe or at the end of the long poll cycle (310 seconds) if no message is published to any of the subscribed channels.
Other GET requests will be due to other PubNub operations like publishes, heartbeats, history, etc.
In case of any questions, contact us at firstname.lastname@example.org.