@youtubemusic I noticed you've been advertising yourself a lot on Google Play Music. So I might as well get this off my chest.
Let me play music in the app with my phone locked and I'll consider downloading and keeping it.
You can definitely listen to music when your phone is locked with the background play feature by subscribing to YouTube Music Premium. Here's more info: https://yt.be/help/saqg . Hope this helps clarify.