High internet traffic or slow internet speeds is the main reason behind this. If someone in your house is using the broadband connection to download or upload something, this can happen. You need to disconnect all users from the broadband connection and try again.

On the other hand, you need to make sure that your device is connected to internet via a direct LAN Ethernet connection. If you are on Wi-Fi, there is a high possibility for you to see buffering. If this is not possible, you should move the device closer to the router.