屏幕在React Navigation中自动导航到上一个屏幕

Question

所以，在我的根index.js文件中，我已经走了这条路

const RootNav = createSwitchNavigator(
  {
    Auth: {
        screen: Auth
    },
    Tabs: {
        screen: TabHolder
    },
  },
  {
    initialRouteName: 'Auth',
  }
);

Auth.js

const Auth = createStackNavigator(
    {
      Splash: {
          screen:Splash
      },
      BeforeLogin: {
          screen:BeforeLogin
      },    
      Signin: {
          screen:Signin,
      },
      ForgotPassword: {
          screen:ForgotPassword
      },
      Signup: {
          screen:Signup
      },
    },
    {
        headerMode:'none',
        mode:'modal', 
    }
  );

TabHolder.js

const TabHolder = createBottomTabNavigator ({
 HomeMainTab: {
      screen: HomeMainStack,
      navigationOptions: { },
},
 ProfileMainTab: {
      screen: ProfileMainStack,
      navigationOptions: { },
},
)}

const ProfileMainStack = createStackNavigator({

      Profile: {
          screen:Profile
      },
      Settings: {
          screen:Settings,
      },
    },
  {
      headerMode:'none',
      mode:'modal',
  },
);

现在，当我使用Settings从Signin屏幕导航到this.props.navigation.navigate('Signin')屏幕时。我导航到Signin屏幕，然​​后立即导航到BeforeLogin屏幕。我不知道为什么会这样。有人请帮我。