Problem with Server process did not cleanly exit within 30 seconds of OnProcessTerminate(), exitCode(-1)

Hi everyone! I receive this error when my Windows c5.large server shutdowns (roughly 15min after the last session has been terminated):

Server process did not cleanly exit within 30 seconds of OnProcessTerminate(), exitCode(-1), launchPath(--), arguments(null), instanceId(--), publicIP(--), gameSessionId(none)

I haven’t noticed any problems while the server is running a game session. The server is built using Unity 2020.2 with the Server Build option. I receive no errors when running the server locally with the simulator agent. I’m checking ProcessEnding() GenericOutcome which returns Success. Here is my GameLift server implementation (pretty much off the shelf):

public class GameLiftServer : MonoBehaviour
{
    private static bool _gameLiftActive = false;
    public static bool GameLiftActive { get => _gameLiftActive; set => _gameLiftActive = value; }

    public void Start()
    {
        var listeningPort = 7777;
        LogWriter.LogMessage("Start called, initializing GameLift.");

        var initSDKOutcome = GameLiftServerAPI.InitSDK();
        if (initSDKOutcome.Success)
        {
            ProcessParameters processParameters = new ProcessParameters(
                (gameSession) =>
                {
                    GameLiftServerAPI.ActivateGameSession();
                },
                (updateGameSession) =>
                {

                },
                () =>
                {
                    LogWriter.LogMessage("OnProcessTerminate callback, server shutting down.");
                    var outcome = GameLiftServerAPI.ProcessEnding();
                    if (outcome.Success)
                    {
                        LogWriter.LogMessage("ProcessEnding() Outcome success");
                    }
                    else
                    {
                        LogWriter.LogMessage("ProcessEnding() Error Name: " + outcome.Error.ErrorName + " Message: " + outcome.Error.ErrorMessage);
                    }
                },
                () =>
                {
                    return true;
                },
                listeningPort,
                new LogParameters(new List<string>()
                {
                    "Server.log"
                })
            );

            var processReadyOutcome = GameLiftServerAPI.ProcessReady(processParameters);

            if (processReadyOutcome.Success)
            {
                print("ProcessReady success.");
                GameLiftActive = true;
                SetupNetworkManager.Instance.StartNetworkingManager("");
            }
            else
            {
                print("ProcessReady failure : " + processReadyOutcome.Error.ToString());
            }

        }
        else
        {
            print("InitSDK failure : " + initSDKOutcome.Error.ToString());
        }
    }

    private void Update()
    {

        // Quit if server 
        if (NetworkingManager.Singleton.ConnectedClientsList.Count <= 0 && Time.time > 600)
        {

            LogWriter.LogMessage("ConnectedClientsList was zero calling Application.Quit().");
            Application.Quit();

        }

    }

    static public void AcceptPlayerSession(string playerSessionId)
    {
        GameLiftServerAPI.AcceptPlayerSession(playerSessionId);
    }

    static public void RemovePlayerSession(string playerSessionId)
    {
        GameLiftServerAPI.RemovePlayerSession(playerSessionId);
    }

    void OnApplicationQuit()
    {

        LogWriter.LogMessage("OnApplicationQuit called, ending gamelift process.");
        var outcome = GameLiftServerAPI.ProcessEnding();
        if (outcome.Success)
        {
            LogWriter.LogMessage("ProcessEnding() Outcome success");
        }
        else
        {
            LogWriter.LogMessage("ProcessEnding() Error Name: " + outcome.Error.ErrorName + " Message: " + outcome.Error.ErrorMessage);
        }

    }
}

My server build has no install dependencies. The server location is eu-central-1 with fleet-id: fleet-7a4dbb81-7e9d-42cf-817d-3ea9834277e4
Thank you