I have this kotlin application. It’s sole purpose is to test if the FCM notifications are received (so the most basic setup here) The problem I have and cannot get a root cause for this is that it takes me multiple times of starting / restarting / stopping the application (and android studio as well), to see on the emulator (Pixel 8 Pro) that indeed those notifications are received. And they really do (the app is in the background for this) and they are received every time once it works, but as I said it takes multiple times of restarting app / android studio and I cannot come to a conclusion what is exactly the case here, and why on first run of the application, then background it, send notification it does not receive those. Any help there? I am not a kotlin / android dev, I just want to test the integration from the backend service that sends those notifications. NOTE: for testing this I am using google console messaging to send notifications.

MainActivity.kt

package com.example.notification_sandbox

import android.os.Bundle
import android.util.Log
import android.widget.Toast
import androidx.activity.ComponentActivity
import androidx.activity.compose.setContent
import androidx.activity.enableEdgeToEdge
import androidx.compose.foundation.layout.fillMaxSize
import androidx.compose.foundation.layout.padding
import androidx.compose.material3.Scaffold
import androidx.compose.material3.Text
import androidx.compose.runtime.Composable
import androidx.compose.ui.Modifier
import androidx.compose.ui.tooling.preview.Preview
import com.example.notification_sandbox.ui.theme.Notification_sandboxTheme
import com.google.android.gms.tasks.OnCompleteListener
import com.google.firebase.FirebaseApp
import com.google.firebase.messaging.FirebaseMessaging
import com.google.firebase.messaging.RemoteMessage

class MainActivity : ComponentActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        FirebaseApp.initializeApp(this)

        enableEdgeToEdge()
        setContent {
            Notification_sandboxTheme {
                Scaffold(modifier = Modifier.fillMaxSize()) { innerPadding ->
                    Greeting(
                        name = "Android",
                        modifier = Modifier.padding(innerPadding)
                    )
                }
            }
        }

        FirebaseMessaging.getInstance().token.addOnCompleteListener(
            OnCompleteListener { task ->
                if (!task.isSuccessful) {
                    Log.w(
                        TAG,
                        "Fetching FCM registration token failed",
                        task.exception
                    )
                    return@OnCompleteListener
                }

                // Get new FCM registration token
                val token = task.result

                // Log and toast
                val msg = getString(R.string.msg_token_fmt, token)
                Log.d(TAG, msg)
                Toast.makeText(baseContext, msg, Toast.LENGTH_SHORT).show()
            })

        
    }

    companion object {
        private const val TAG = "MainActivity"
    }
}

@Composable
fun Greeting(name: String, modifier: Modifier = Modifier) {
    Text(
        text = "Hello $name!",
        modifier = modifier
    )
}

@Preview(showBackground = true)
@Composable
fun GreetingPreview() {
    Notification_sandboxTheme {
        Greeting("Android")
    }
}

Then a service that handles notifications:

package com.example.notification_sandbox

import android.util.Log
import com.google.firebase.messaging.FirebaseMessagingService
import com.google.firebase.messaging.RemoteMessage

class MyFirebaseMessagingService : FirebaseMessagingService() {

    override fun onMessageReceived(remoteMessage: RemoteMessage) {
        // Handle FCM messages here
        Log.d(TAG, "From: ${remoteMessage.from}")

        // Check if the message contains data
        remoteMessage.data.isNotEmpty().let {
            Log.d(TAG, "Message data payload: " + remoteMessage.data)
        }

        // Check if the message contains a notification payload
        remoteMessage.notification?.let {
            Log.d(TAG, "Message Notification Body: ${it.body}")
        }
    }

    override fun onNewToken(token: String) {
        // Handle new or refreshed FCM registration token
        Log.d(TAG, "Refreshed token: $token")
        // You may want to send this token to your server for further use
    }

    override fun onCreate() {
        Log.d(TAG, "started!!!")
    }

    companion object {
        private const val TAG = "MyFirebaseMsgService"
    }
}