Audio Snapshot TransitionTo Not Working in Awake and Start

I got around this issue by calling the transition a frame later. Start a coroutine in your awake, wait a frame then fade in. Here is how your script would look.

     using System.Collections;
     using System.Collections.Generic;
     using UnityEngine;
     using UnityEngine.Audio;
 
     public class JKDefaultSnapshot : MonoBehaviour
     {
         public List<AudioMixerSnapshot> snapshots;
         public float transitionTime;
 
         void Awake ()
         {
             StartCoroutine( TransitionToSnapshots() );
         }
 
         private IEnumerator TransitionToSnapshots()
         {
             // we wait for 1 frame then fade in, and then it works.
             yield return null;
 
             foreach(var snapshot in snapshots)
             {
                 snapshot.TransitionTo(transitionTime);
             }
         }
     }