Why won't Groove recognize some of my music files?

[Windows Central Question]

I have a lot of albums on my hard drive That I'm trying to add to Groove. For some reason, Groove will not recognize the items when I go to add them. The cuts are all mp3s and play through the Creative MediaSource, so I know the files aren't corrupted. Does anyone know what could be preventing the music from being added to the Groove playlists? And how do I fix it?