Hi there. YT automatically adjusts the quality of streaming from standard to high definition based on the speed of your internet connection. You can manually adjust the video quality of any video you're watching on a computer or mobile device. Here's how: https://goo.gl/SjLYNp
Thanks for trying those steps. Please file a feedback report from YouTube here: https://goo.gl/WdI0BK . You may not get a direct response, but we do review all of the feedback and use the details to investigate and fix issues. Appreciate it!