I hate how @YouTube changes the list of videos shown on the right as it plays the next video.
Many times I want to watch the videos shown on the right, but if I click the "next track"
video controls the list that was there changes to one based on the newly current video.
You create an expectation of seeing them in order by having them in a column under the heading "Next Up". One thin line separater doesn't make it clear that "Next Up" only applies to top video. Borders, spacing, section names for every section, and colors make UIs clearer.