Android Studio. Screen flicks after activity changing

Question

After i changing activity in my nav header, i have strange flickers and i want to get rid of them:

Im not sure which part of code should i show, but guess that problem could be in how intents are creating or something like that. Here is a code of my navigation buttons:

@Override
public boolean onNavigationItemSelected(MenuItem item) {
    // Handle navigation view item clicks here.
    int id = item.getItemId();

    if (id == R.id.main) {
        Intent main = new Intent(main.this, main.class);
        main.setFlags(Intent.FLAG_ACTIVITY_REORDER_TO_FRONT);
        startActivity(main);
    } else if (id == R.id.find_friends) {
        Intent findfriends = new Intent(main.this, FindFriends.class);
        findfriends.setFlags(Intent.FLAG_ACTIVITY_REORDER_TO_FRONT);
        startActivity(findfriends);
    } else if (id == R.id.followers) {
        Intent followers = new Intent(main.this, Followers.class);
        followers.setFlags(Intent.FLAG_ACTIVITY_REORDER_TO_FRONT);
        startActivity(followers);
    } else if (id == R.id.follow) {
        Intent follow = new Intent(main.this, Follow.class);
        follow.setFlags(Intent.FLAG_ACTIVITY_REORDER_TO_FRONT);
        startActivity(follow);
    } else if (id == R.id.statistics) {
        Intent statistic = new Intent(main.this, statistic.class);
        statistic.setFlags(Intent.FLAG_ACTIVITY_REORDER_TO_FRONT);
        startActivity(statistic);
    } else if (id == R.id.LogOut) {
        FirebaseAuth.getInstance().signOut();
        Intent mainact = new Intent(main.this, MainActivity.class);
        mainact.setFlags(Intent.FLAG_ACTIVITY_REORDER_TO_FRONT);
        startActivity(mainact);
    } else if (id == R.id.About) {
        Intent about = new Intent(main.this, About.class);
        about.setFlags(Intent.FLAG_ACTIVITY_REORDER_TO_FRONT);
        startActivity(about);
    }

    DrawerLayout drawer = findViewById(R.id.drawer_layout);
    drawer.closeDrawer(GravityCompat.START);
    return true;
}