Several things can cause buffering on an Nvidia Shield. Here are a few troubleshooting steps to help you find and solve the problem:
Check your internet speed. You’ll need at least 5 Mbps of download bandwidth to stream video from many services. VPNs can slow down your internet as well, so if you find that buffering increases while connected to the VPN, try a different server or provider. An Ethernet connection will usually offer faster and more reliable speeds than Wi-Fi. If you’re using an ethernet connection, be sure to toggle the Ethernet switch on in the settings.
Update your Nvidia Shield and applications. Older versions of streaming apps and the Nvidia Shield operating system (Android) might struggle to stream efficiently. Be sure your OS and apps are all up to date. You can update apps through the Google Play Store if they aren’t set to automatically update. Some users have found success in reinstalling troublesome apps.
Disable or modify apps that affect internet routing. VPNs, pi-hole, custom DNS servers, ad blockers and other apps that affect your internet connection can interfere with playback. Try turning them off and on again one by one to narrow down the culprit.
Reboot. Completely reboot the Nvidia Shield; don’t just put it into sleep mode. Likewise, you can reboot your wi-fi router and internet modem.
Reset the Shield. When all else fails, perform a factory reboot on the shield.