Corountines and messaging system

Hello, In our project we're using CSharpMessenger and encountered an interesting bug. We're getting an exception when a broadcasted message starts a coroutine. We need coroutines to be able to delay execution of some parts of the code, using WaitForSeconds. When not using messaging system, everything works as expected:

 public class GameStateManager : MonoBehaviour {
     void Start ()
     {
         StartCoroutine( StartGameCorountine() ); //Will be executed in parallel
     }
 
     private IEnumerator StartGameCorountine()
     {
         yield return new WaitForSeconds(0.5f);
 
         //Some code to actually start the game
         //...
         //...
     }
 }

But when we introduced the messaging system we started getting MissingReferenceException saying:

MissingReferenceException: The object of type 'GameStateManager' has been destroyed but you are still trying to access it.

Here's our code using the messaging system:

 public class GameStateManager : MonoBehaviour {
     void Start ()
     {
         Messenger.AddListener("start game", StartGameMessageHandler);
         Messenger.Broadcast("start game");
     }
     
     void StartGameMessageHandler()
     {
         StartCoroutine( StartGameCoroutine() );    //The exception rises at this line.
     }
     
     private IEnumerator StartGameCoroutine()
     {
         yield return new WaitForSeconds(0.5f);

         //Some code to actually start the game
         //...
         //...
     }
 }