So i asume the youtube app on the xg1v4 is not 4k since stats for nerds says 1080p.
The version for You Tube might be different than You Tube version found on My Sumsung UHD television's apps, along with other brands of UHD televisions that have a You Tube app.
Does your "stats for nerds" remark mean when you use "select" button on remote to see buffer window, you see only HD icon after the 4K heading shown as part of the title?
After getting the Buffer window, click on Options found on line below buffer line, and then click on 4K just left on "Options". That might say "1080P". Click on 2160p to force 2160p output from You Tube video player.
Now; if you only see "1080p" as an option in the resolution list, then "You Tube" does not recognize your 4K DVR as being capable of receiving the 2160p out-put. Use your UHD television's "You Tube" app to see if you can actually get 4K over your current Internet broadband. Please note that the latest version of You Tube (found on my tv) does not automatically output the 4K signal to a 4K tv. I have found 240p signal output from You Tube, and need to switch to 2160p for correct output. Also; some people from other countries have mistakenly uploaded in wrong resolution their 4K video. A day or two later the actual 4K copy shows up.
I assume You Tube is working on their program to make thing work easier. Their latest version from 3 to 4 weeks ago meant to show people that you could always force the highest the highest resolution possible for the device you were using. They can't be accused of down-grading the resolution.
Anyone with insufficient broadband will lock up the video with "loading", and need to choose a lower resolution to play a video without problems.