Confused About Change in Playlist's Ability to Play Seamlessly

I'm a big fan of building a playlist to watch several videos one after another on YouTube; and up until a few days ago, if I clicked on a video or back to the main page, the playlist would continue playing in the lower right corner of the screen, seamlessly.

Now if I try to click away at all, everything just stops. What changed, and how do I change it back?