I have good news everyone!
I'm not entirely sure what changed in the YouTube download URLs, but I have discovered an alternate solution for obtaining Vevo download links (as well as regular YouTube video links).
At the moment, I'm busy testing the new code on both Linux and Windows, for both the free and paid-for versions.
Soon I will be pushing out new versions of my software, and I will notify you here when these new versions are available.
Thank you for your patience, and stay tuned!