This sounds like a problem I had a while back. The fix for me was the solution posted in this thread: Android Chrome's loss of sound
For me, if my game was allowed to sit for a few minutes of inactivity then music and/or sfx could occasionally stop working. This would happen if I left the game open in the menus, in a level, paused, with an add open. Basically in any stage of the game.
I followed the fix in the thread above and it solved the problem. It involves making an inaudible sound play once every second throughout the game.
Im not sure if thats the scenario you are experiencing. For me it involved a delay. Like, if I put my phone down for 1-2 mins, then came back to the game, the sound or music might have stopped working. If you're experiencing something more immediate, like going straight from the leaderboards back to the game within just a few seconds, with no delay involved, it's probably not the same issue. In that case, as you say it might be to do with the events you have to start / stop music... although your sfx shouldnt crap out... the fact that your sfx stop working suggest it *could* be the same bug discussed above... coz its not like you have to turn the sfx on / off, or pause them like you do with music.