I have a 200 mbps down connection at home, and my phone LTE connection is around 25mpbs, but on my laptop, desktop, iPad, and my phone, Youtube never maxes out the resolution to match the display resolution. Speedtest on all devices hit the max of what my connection is capable of. The only apps that seem to work properly are on my 65KS8000 and my PS4(occasionally, usually doesn't kick in until about 10 seconds later on PS4), which is funny since these apps don't even let you pick the resolution. They just figure it out. Every time I have to click on the option to select the max resolution. My Galaxy S8 is also weird because there are times when it won't even let me select 1440p, 1080p is the max, but then it randomly offers me the option on the same video a day later.