My Problem with Android and Music

Say I've bought an album on bandcamp from my phone, and I want to download it to my phone. Fine. It gets sent as a zip file, and I can properly extract it and move it to a folder. My problem is that when I go to the Google Play Music app, it does not show up under local media. I can play it through the File Manager, but that becomes a hassle as I can't exit the app or even turn off the screen without the song pausing. However, if I were to download that song from my computer and copy it over to my phone, Google Play Music works at it should, and the song shows up and plays.

I know it's not any DRM, because the MP3s in question are the same whether downloaded through the computer or phone. It's not the app's fault, because similar things happen with Shuttle+ Music player. Downloaded directly, the song will not play at all in the app and won't show up in the library. Downloaded and copied, the music plays perfectly. I also know it's not the extraction process, because I can literally download directly to the phone, copy it to the computer and copy it back to the phone, and there are no problems.

This leads me to think there is something on an OS level preventing me from playing the directly downloaded music. Any ideas?