Inconsistent results with music and synchronization

Hello there,

I'm having some minor issue with my game. I have a screen that show the score in a coroutine when the level is over and a music is playing. The thing is I want the music to be synchronized with some sound effects and it should be quite easy as the tempo is 120 (2 beats per sec). But the problem is sometimes for a reason I don't really understand the sfx and the music are not synchronized. Here is the code:

   IEnumerator WinLevel()
         {
             //many things before
             PlayWinMusic();
             missionComplete.gameObject.SetActive(true);
             yield return new WaitForSeconds(2f);
             missionComplete.gameObject.SetActive(false);
             endLevelBoard.DisplayEndLevelBoard(Mathf.FloorToInt(timer), timerBonus, GameControl.livesCount, livesBonus, perfect, perfectBonus, total);
         }
     void PlayWinMusic()
     {
         MusicScript.instance.SetTrack(TrackType.Win);
         MusicScript.instance.PlayMusic();
     }
 
  public void SetTrack(TrackType type)
     {
         switch(type)
         {
             case TrackType.Menu:
                 clip=Resources.Load("Menu") as AudioClip;
                 break;
             case TrackType.Overview:
                 clip=Resources.Load("Overview") as AudioClip;
                 break;
             case TrackType.InGame:
                 clip=Resources.Load("InGame") as AudioClip;
                 break;
             case TrackType.Win:
                 clip=Resources.Load("Win") as AudioClip;
                 break;
         }
     }
 
  public void PlayMusic()
     {
         if(!music.isPlaying)
         {
             music.clip=clip;
             music.Play();
         }
         else
             StartCoroutine(WaitForPlay());
     }
 
     IEnumerator WaitForPlay()
     {
         while(music.isPlaying)
         {
             yield return null;
         }
         music.clip=clip;
         music.Play();
     }
     

I won't post the endLevelBoard function because if the missionComplete image appear in the right moment then everything follow nicely. So the problem basically happens between PlayWinMusic(); and missionComplete.gameObject.SetActive(true);

By the way it is absolutely sure that music is not playing when I call PlayWinMusic() so it's not going in the while(music.isPlaying) loop and therefore not in the yield return null.