Why is an Apple Music song's adlib disappearing and reappearing?

One of the songs I listen to has a specific adlib before a lyric, and for a while I couldn't hear it in the song. The lyric still pops up in the lyric screen, but I couldn't hear it. Then, it came back for about a month. Now it's gone again. Why is it doing this?

[Re-Titled by Moderator]