I also have this problem. New budget TCL 4K Google TV, can't handle Twitch at anything higher than 720p if I'm lucky. 1080p stutters every few seconds.
The TV can play 4K content from Youtube, Amazon Prime, Netflix, etc with no stuttering or buffering, so the TV (and my network) is clearly capable of 4K bandwidth.
My PC on the exact same network can handle Twitch at 1080p with no stuttering, so my network can clearly handle 1080p from Twitch.
The only thing left that could be causing this is the app.
I also have this problem. New budget TCL 4K Google TV, can't handle Twitch at anything higher than 720p if I'm lucky. 1080p stutters every few seconds.
The TV can play 4K content from Youtube, Amazon Prime, Netflix, etc with no stuttering or buffering, so the TV (and my network) is clearly capable of 4K bandwidth.
My PC on the exact same network can handle Twitch at 1080p with no stuttering, so my network can clearly handle 1080p from Twitch.
The only thing left that could be causing this is the app.