Same issue here forUE55NU8002. Is this some kind of a joke to break basic functionality like this and do nothing after 2 weeks of problems being reported?
This Firmware is truely BUGGY LIKE 
. Exactly, in fact that Firmware destroyed, yeah devastated 4K Viewing Experience on my 8k Q900 (2018). That's such a most critically, ugly mistake of that company. By this practice, they Will Loose a LOT of customers, for sure. Not because of that silly YT app which even cannot play 8k on an 8k TV. No. Their update philosophy, is just like noobs would do. Are there any Test methods at Samsung? Why i pay 4000€ and you engineers give me such a bad feeling when using Samsung Products?
I definitely will look out for other manufatures in the future. Let's see when the final firmware will be deployed which makes the TV unusable slow and they try to make people think, oh, the TV got old, have to buy a new samsung TV." Yes, let's  the earth and it's resources.
Funny thing, when the Firmware update was showing up on the Q900 8K TV, i selected "do not install now". And even Automatic Updates are OFF, the TV updated the firmware without my confirmation. And that happened after i found out that this firmware has a BIG issue.
Unbelievable, Samsung treat their Customers as Beta Firmware Testers (or even Alpha?).
By the way, send me a new Remote, that beautiful shiny piece of technology works like  ah, forget it.
Samsung, i expect Your Apologize and a Solution ASAP!
Just thought I'd add my input if it's any help. I have a 55NU8000 (UK) and have updated to 1310.4.
I like to have a quick browse online for issues before each fw update, and this time was no different. I did the update anyway, but I can report I have been on YouTube app and tried many 4k/60 videos since, and playback is fine, no issues at all.
I do not have a problem with any 4k YouTube video that is part of generally available free content - movie previews and 4k demonstrations etc. The only video I have an issue with is the only 4k video I actually bought/own! I didn't actually realise you could watch movies bought via Google Play Movies through YouTube until I saw this issue reported! I still firmly believe it is a Google issue and not a Samsung issue. Google are absolutely awful at tampering with stuff and not telling anyone they've done it or what they've done or what problems exist with their systems.
It's probably not an issue with YT, even 4k YT in the noob Internet Browser has the same issue. Actually i figured out what the issue is. And also found a bloody workaround, so, SAMSUNG, go and fix that Issue ASAP ! If you, Samsung wanna get my help, put me on your salary list !