Some videos work, some don't.

Downloading, or at least attempting to, from YouTube has been kind of iffy lately. I copy a YouTube URL, and I know when it works, because it will almost immediately stick the video name and length into the URL bar in VDownloader. These are the videos that I can download with no issues whatsoever.

But some videos aren't working at all. The real URL stays there, or, in rare cases, it does change, but it takes a while. Then, when I click to download, I either get "This video is unavailable" (which is peculiar because that's incorrect; I can access the public video, not private or even unlisted, in my standard browser just fine)  or "Unable to obtain required initial information about this video". Those errors occur interchangeably, even on the same video. Sometimes, I can get as far as actually clicking the save button, and then it throws an error while preparing the download.

It's not only annoying, but also incredibly confusing. Why are only some YouTube videos working?