Weird problem with playlist

Something very strange is happening with a playlist I made. It's a YouTube playlist of several hundred songs that I like listening to *(over 900).* For some reason, the playlist works fine most of the way through, but when I get pretty deep into the list *(like, past the 400th one)* it will go to the next video, but the playlist will disappear. Like, it will play the video but there's no playlist on the side of the screen, so it won't go to the next song after that one. It's as if I just clicked on the video without any playlist whatsoever. And it's not just if I've been listening to the playlist for hours on end either - I can pull up my playlist, scroll down to video 400, click on it, and then I'm watching that video without any playlist at all. This is really annoying. Any idea how to fix it?