This is a bug, I know its been reported, and I'm really disappointed it has not been cleared yet. The only known workaround to this is to not have any sound playing when the DM leaves the game(this also includes refreshes). This is really annoying cause there are other bugs out there like the tokenmod UI crash bug when you try to set default tokens of sheets that are open by other players in the session. If you want to cure the problem after its already affecting you, you have to delete that specific sound file from the session then readd it. If you use Roll20AM, that also means you need to "remove all", "import jukebox", and adjust any settings to playlists you had setup. I know, this is really annoying, I agree.