Source code for AudioMixerSnashot available?

As it says in the title.

 

I haven't used the objects you are referencing, but this is my go-to for timing in Unity3D:

https://docs.unity3d.com/Manual/ExecutionOrder.html

If your script code is calling stuff in those mixers, or if the mixer docs say certain things happen at certain times in the update loop, perhaps the above graph can give you an idea of what is going on.