I have an issue in FMOD Studio (1.06.18) where lowering the volume of an event instance does not affect the volume of a nested event inside. This does only happen for one specific event, but I can’t determine the cause. Setting the volume of the parent instance with eventInstance->setVolume(0) does not have any effect. Lowering the volume in the graphical GUI of FMOD Studio of the parent event does not have any effect on the nested event either. However, increasing the volume does have an effect.
I haven’t been able to reproduce this issue using a simple example (a nested event playing a single sound). If the problem appears persistent and can be reproduce consistently, I would recommend sending us a copy of the event in a new project to email@example.com. Alternatively, if the setup is fairly simple, you can post screen capture of the parent event and nested event.