YouTube video displayed in fuzzy low resolution on a hi-def smart TV

We always enjoyed nature videos and concerts in Hi-Def from YouTube over AT&T UVerse. A few weeks ago all these videos started to display in fuzzy low resolution on our 4K smart TV.  This coincided with news reports about internet providers being allowed to reduce bandwidth delivered to certain users.  

After checking all the menus and settings on the TV, chatting with a tech on the AT&T website, and not finding a reason or solution, we called the AT&T Help desk. Sarah was very thorough in her troubleshooting and conducting a speed test on our laptop.  After an hour we concluded that the cause was at our house, and she suggested we see if switching from wi-fi to ethernet would make a difference.  We tried that, and the YouTube video was still smeared and fuzzy.

Finally we poked around the YouTube screen with the TV remote mouse and discovered a hidden row of buttons at the bottom including a 'quality' setting.  After several clicks with no effect, a menu came up to reveal that one of us had selected the 140p resolution without knowing it. We selected the 'auto' setting which returned the current video to 1080p and totally solved the problem.

I'm writing this to recognize and thank the Help desk for Sarah's patient and thorough efforts, which traced the problem right back to our own lap. Also this might perhaps save someone else the agony of thinking the web is robbing their bandwidth.