I know that Apple docent support VP9 which may be part of the problem but watching Impulse S01E02 last night was almost unwatchable. Dark scenes especially, were pixelated and lots of colour banding. Basically looked like two blobs talking to each other.
I tested on two Sony TV's one 2015 LCD and the other an A8F OLED and they both look the same. Also tried both Wi-Fi and Ethernet but no change. The same video looks fine on Safari on my iMac using the same internet connection so I don't think its a connectivity problem plus all other streaming apps look fine.
If anyone has Youtube red and wants to take a look, the worst of it is around the 30 minute mark when they are in the car at night.