Well there are two different bugs that I know of.

One is to do with starting an event (either online or offline) and there is no music, only SFX. Happens every so often (more now than ever thanks to bugs and insects).

The other one is simply to do with specific songs not playing. I went through one of my playlists and found that there were at least 10 tracks that NEVER play, even if you select them manually. Game just goes mental and skips song (or doesn't play anything if you make a separate playlist full of bugged songs ).

Weird eh?