Here is an example:
A scene is loaded with four symbols on two lines of musical stave, 2 bass drums and 2 snare drums. If you press 'play', the timeline starts and each symbol briefly scales up then down in sequence and the appropriate drum audio file is meant to play with each of the symbols.
What actually happens is the timeline plays but no audio occurs. If you press each symbol, the correct audio is triggered and then if the 'play' button is touched after this, that sound is then played in the timeline, if you only press one of the snare drums, only the snare drums will then play in the timeline, but both snare drum symbols will sound off.
It's as if the program requires, as you say, each sound to be manually triggered or 'unlocked' initially by a user, but before the latest xCode & iOS11 upgrade, this wasn't the case, they would behave as they do in the browser test phase.