Ever since Second Life Viewer (7.1.9.10495892574) parcel music has been hard to start. It's fairly repeatable but not guaranteed. _Sometimes_ changing regions out and back will fix it. Always relogging will fix it. Coincident with this, application audio capture apps (I use Rogue Amoeba's Audio Hijack) are no longer able to capture SL audio output.
The impact is severe for my DJ work. Both symptoms make it very hard to monitor in-world audio.
PS I have the folks at Rogue Amoeba looking into this too, but as they use the new macOS audio capture API the solution is probably in the hands of Linden Lab and/or Apple. I am hoping you can roll back/fix whatever commit broke this.