On your home laptop or desktop open up a web browser and enter http://bthomehub.home or click here. This should take you to your homehub admin panel. Then click on Advanced Settings.
You will be asked for an admin password, you can find this on the card usually found on the back of your home hub.
Once you've entered your password make sure you have Advanced Settings selected then click Home Network and Smart Setup. Ensure the No option is selected then click Apply.
Once you have gone through these steps try using your Chomecast once again and see if it has resolved the problem.