Correctly check if user is logged in. Android

I have my login setup like this, I use retrofit to authenticate from the server and I'm using a token api authentication:

In the MainActivity.java method onCreate

apiInterface = ApiClient.getClient().create(ApiInterface.class);

User user = SharedPreferencesHelper.getUser(MainActivity.this);

if (user.getToken() == null) {
    Intent login = new Intent(MainActivity.this, LoginActivity.class);
    startActivity(login);
} else {
    setContentView(R.layout.activity_main);
    buildMain();
}

In the LoginActivity.java method on create (I'll summarize, the code is quite long)

loginbtn.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {
        //get login ingo

        Login login = new Login(scardI, passwordI, device_name);

        Call<User> call = apiInterface.LoginUser(login);

        call.enqueue(new Callback<User>() {
            @Override
            public void onResponse(Call<User> call, Response<User> response) {
                if (response.isSuccessful()) {
                    User user = response.body();
                    //save user info into SharedPreferences
                    SharedPreferencesHelper.setUser(LoginActivity.this, user);
                    
                    //check if user saved correctly by getting the user token
                    if (SharedPreferencesHelper.getUserToken(LoginActivity.this) != null) {
                        finish();
                    }
                } else {
                    //show error message
                }
            }
            @Override
            public void onFailure(Call<User> call, Throwable t) {
                //show error message
            }
        });
    }
});

I'm having an issue, after the user logs in a blank page is displayed instead of the activity_main.xml however when I close the app and reopen it it takes me straight to the activity_main.xml as expected. Is there a reason that after the login it doesn't take me to the activity_main like expected.

An intent to MainActivity.java is missing on success. A blank screen is displayed because finish() is called.

 if (response.isSuccessful()) {
     User user = response.body();
     SharedPreferencesHelper.setUser(LoginActivity.this, user);
      if (SharedPreferencesHelper.getUserToken(LoginActivity.this) != null){
       Intent i = new Intent(this, MainActivity.class);
       i.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK | Intent.FLAG_ACTIVITY_CLEAR_TASK)
       startActivity(i);
}
                    
}