startActivity(Intent) is destroying activity every time, why?

Question

As the title says, usually onDestroy() is only called if the phone needs to free up memory.

My flow: Activity (A) sets a recurring Alarm to send a notification to the user in A's onCreate method:

public void startEMAAlarm(){
    Log.d(TAG, "startEMAAlarm: in start ema alarm");

    Calendar cal = Calendar.getInstance();
    long when = cal.getTimeInMillis();

    cal.setTimeInMillis(System.currentTimeMillis());
    cal.set(Calendar.HOUR_OF_DAY, 8);
    cal.set(Calendar.MINUTE, 30);

    AlarmManager alarmMgr = (AlarmManager) getSystemService(Context.ALARM_SERVICE);
    Intent intent = new Intent(this, EMAAlarmReceiver.class);
    startEMAIntent = PendingIntent.getBroadcast(this, 0, intent, 0);
    alarmMgr.setInexactRepeating(AlarmManager.RTC_WAKEUP, cal.getTimeInMillis(), 1000 * 60 * 20, startEMAIntent);
    Log.d(TAG, "startEMAAlarm: alarm shjould be set");
    alarmStarted = true;


}

The alarm receiver gets this, sends a notification, and if the notification is selected, it starts activity B:

EMAAlarmReceiver: OnReceive{

Intent resultIntent = new Intent(context, EMA.class);
        //resultIntent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK | Intent.FLAG_ACTIVITY_CLEAR_TASK);
        PendingIntent pendingIntent = PendingIntent.getActivity(context, 0, resultIntent, 0);

        NotificationCompat.Action action = new NotificationCompat.Action.Builder(R.drawable.cdmh_small, "SNOOZE", snoozePendingIntent).build();

        Notification mBuilder =
                new NotificationCompat.Builder(context, CHANNEL_DI)
                        .setSmallIcon(R.drawable.noti_icon)
                        .setContentTitle("EMA")
                        .setAutoCancel(true)
                        .setContentText("Time for another EMA :)")
                        .setOngoing(true)
                        .setChannelId(CHANNEL_DI)
                        .setSound(uri)
                        .setContentIntent(pendingIntent)
                        .addAction(action)
                        .build();

        mNotificationManager.notify("first",1, mBuilder);
        Log.d(TAG, "onReceive OREO: should be notification built now");

The notification then appears on the phone, but as soon as I click it, Activity A has its onDestroy() method called, and I am not sure why.

It does not really matter, because i can use savedInstance etc to recreate it later ( ie Activity B returns to Activity A via another Intent when leaving), but I am not sure why it is being destroyed at that point. As you can see I am not currently using any flags, but I have experimented with lots of them, and it does not seem to change the behavior.

Not sure if it matters, but Activity B is just a collection of SeekBars the user slides over, it then saves their value to a text file, and returns to Activity A

How Activity A looks in Manifest:

<activity
        android:name="com.anysoftkeyboard.ui.settings.setup.FinishInstallScreen"
        android:screenOrientation="portrait">

How activity B looks:

<activity android:name="com.radicalninja.logger.EMA"
              android:screenOrientation="portrait"/>

Answer 1

Ok, for anyone else that may randomly come across this problem, it was caused by my own stupidity.

Basically I had made some changes to my application, and had forgot to update the TaskStackBuilder part of my notification, so I was building the Parent Stack incorrectly.

This caused the calling activities onDestroy() method to be called everytime.