Alarm Manager doesn't work with Android API 25

Hi. I have a problem with Alarm Manager that doesn't fired my schedule notification.
using Android.App;
using Android.Content;
using GNote.Android;
using GNote.Droid;
using GNote.Converters;
using System.Collections.Generic;
using Xamarin.Forms;
using GNote.Droid.Models;
using Android.OS;
using GNote.Res.SQLite;
using Android.Icu.Util;
using System;
using GNote.Models;

[assembly: Dependency(typeof(MyNotification))]
namespace GNote.Droid
{
    class MyNotification : INotification
    {
       private List<Note> ListNotes;
       Intent alarmIntent;
       DateTime baseTime = new DateTime(1970, 1, 1);

        public async void CreateScheduleNotifications()
       {
            ListNotes = await DataBaseService.getTimeActiveNotes();
           foreach(Note note in ListNotes )
            {
                long scheduleAlarmTime = this.setScheduleAlarmTime(note.AlarmTime);

                this.addNewScheduleNotification(note.Id,note.Title,note.Content,scheduleAlarmTime);
            }
        }

        private void addNewScheduleNotification(int id,string title, string content,long alarmTime)
        {
           alarmIntent = new Intent(MainActivity.AndroidContext, typeof(AlamReciver));

            alarmIntent.PutExtra("id", id);
            alarmIntent.PutExtra("title", title);
            alarmIntent.PutExtra("content", content);

            var PI = PendingIntent.GetBroadcast(MainActivity.AndroidContext, id, alarmIntent, PendingIntentFlags.CancelCurrent);
            AlarmManager alarmManager = (AlarmManager)MainActivity.AndroidContext.GetSystemService(Context.AlarmService);
            alarmManager.Set(AlarmType.RtcWakeup, alarmTime, PI);
        }

        private long setScheduleAlarmTime(DateTime noteAlarmTime)
        {
            TimeSpan calcTime = noteAlarmTime - baseTime;
            return (long)calcTime.TotalMilliseconds;
        }
    }
}

My "noteAlarmTime" format is (y,m,d,h,m,s).

It works perfect on emulator with API 23 but when I launch app on API 25 then nothing happen.
During testing I noticed something is wrong with this line:

alarmManager.Set(AlarmType.RtcWakeup, alarmTime, PI);

When I change it to:

alarmManager.Set(AlarmType.ElapsedRealtime, SystemClock.ElapsedRealtime() + 5 * 1000, PI);
then notification was displayed.

So, is my time calculation is wrong? Or is different time system between API 23 and 25.

Or problem is somewhere else.

Thank you.