Delay between app process start and Application onCreate

I'm working on an application with large codebase. The problem is that when I launch the app from cold start state, It takes a lot of time to show the first screen of the app.
Based on here I checked the TTID for the app and it was terrifying:

Displayed com.example.myapp/.ui.MainActivity: +6s501ms

So I put some logs to check where is the problem:

class MyApp : Application() {
    override fun onCreate() {
        Log.d("Performance", "MyApp::onCreate::start")
        super.onCreate()
        // App initializations
        Log.d("Performance", "MyApp::onCreate::end")
    }
}

class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        Log.d("Performance", "MainActivity::onCreate::start")
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        // Ui initializations
        Log.d("Performance", "MainActivity::onCreate::end")
    }
}

After this I realized something strange:

---------------------------- PROCESS STARTED (4572) for package com.example.myapp ----------------------------
13:58:06.819 Performance    D  MyApp::onCreate::start
13:58:07.066 Performance    D  MyApp::onCreate::end
13:58:07.132 Performance    D  MainActivity::onCreate::start
13:58:07.566 Performance    D  MainActivity::onCreate::end

I noticed a strange thing. That there is a lot of delay (about 5 seconds) between PROCESS_START and App:onCreate (there isn't any timestamp for PROCESS_START but I calculated manually). Also app creation and activity creation does not take more than 1 second.
So how can I solve this problem? What can be the cause of this issue?

from Delay between app process start and Application onCreate