My TCL/ROKU television was having connection and buffering issue. Some apps such as Youtube was working but Netflix would buffer and hung up with error. The TV would indicate Network connection is working but there's no internet.
Solution is to check your router. Make sure port 5223, 20, 21 are working and not blocked.
I have the same problem when using the Netflix app on the TCL. The sound cuts out randomly and that makes it unwatchable for me. Instead when I use Netflix, I use my Apple TV. When you read this know that The support team of TCL is doing nothing about it and ignores you. PLEASE GO MASSIVELY ON RETAIL SITES LIKE AMAZON and AND RATE THE TCLs!! In my case, I gave the TCL a bad rating! and my next 2 tvs were another brand.
This problem is due to updates. My TCL updated and audio was so bad I could only watch OTA. Unfortunately it's impossible to stop ROKU updates. ROKU is competing against content providers like Netflix and Amazon prime so they degrade the competition.
Why give ROKU more money?? I do not understand. They purposefully built a system architecture that would not work well or at all! I wish folks would understand how business works. They wanted you to buy more ROKU stuff! A $50 Amazon Firestick into the HDMI even without an ethernet extender and over WIFI works incredibly well, it is cheaper, has a much smaller profile (about twice the size of a thumb drive). If I were you refund the ROKU for a firestick.
Came across this post while searching for buffering issues with my new TCL/Roku 65R635 TV. Netflix works perfectly with no issues, but having buffering issues with Sundance and Showtime channels through the YouTube TV app. Anybody seeing similar issues?