[gear54rus]

This might be due to the fact that corporate shitheads decided to take down one of the videos you added.

I've seen such videos transform into [video removed] in custom playlists (which is infuriating to no end, you can't even know what the video was about to look it up somewhere else), maybe it causes videos to disappear from Watch Later entirely.

[code_duck]

Right, for normal playlists YouTube leaves a placeholder saying that there was a deleted video. The frustrating thing about how they do it is that there’s no indication what the video was, unless you remember. Does it handle Watch Later differently? I do know that it seemed to have odd or buggy behavior which is why I stopped using it.

[userbinator]

If you want to really be able to "watch later", I recommend downloading the video.