On iPhone, FMOD version is 1.10.06, a bgm is playing. When I play some other sound, the bgm may mute for a while. Trough the profiler, I found so many instances are playing, it may be the reason that cause this problem.
I think this may be related to an issue that was fixed in 1.10.11, you will need to update to get the fix:
- Studio API - Fixed fire and forget event instances not releasing when another instance of the same event is active.