Probably because of your internet connection. YouTube TV, or any TV streaming service, transfers a large volume of data. First make a physical checking of your internet connection to ensure any connected cables are secure. Ditto for Wi-Fi devices. If all looks fine there, close out all your open apps on your screen and restart your device. Log into your Wi-Fi account and check the Device List to see if you have any unnecessary devices online. Make sure you’ve identified all online devices correctly before disconnecting any from the internet. For example, Log back into YouTube TV and see if the buffering has resolved.