Having a Unity FMOD integration that has a different minor version to FMOD Studio can have unexpected behavior. I would suggest updating your Unity integration version to match your FMOD Studio version.
There are a couple of ways you could go about this. Firstly using Snapshots (FMOD Studio | Glossary). Snapshots will allow you to mute groups during runtime. Another option is pausing individual group buses via code, (FMOD API | Studio API Reference).
If you need any more information about either option please let me know!