Почему Recyclerview выводит со второго раза?

При переходе на новое активити recyclerview вообще не отображается, если выйти назад и зайти снова, то список без проблем подгружается из firebase. В чем может быть проблема?

public class Comments extends AppCompatActivity implements GoogleApiClient.ConnectionCallbacks {

private String str_title = "Отзывы";
private EditText edt_comment_name, edt_comment;
private TextView showComment, hideComment;
private RelativeLayout layout_comment, layout_comment1;

List<User> userList;
private RecyclerView recyclerView;
private RecyclerAdapterUser adapter;

private DatabaseReference mDataBase;

private String USER_KEY = "User";


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_comments);

    final Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);
    final ActionBar actionBar = getSupportActionBar();
    if (actionBar != null) {
        getSupportActionBar().setDisplayHomeAsUpEnabled(true);
        getSupportActionBar().setTitle(str_title);
    }

    recyclerView = findViewById(R.id.rv_comment);

    LinearLayoutManager layoutManager = new LinearLayoutManager(this);
    recyclerView.setLayoutManager(layoutManager);
    userList = new ArrayList<>();

    adapter = new RecyclerAdapterUser(userList);
    recyclerView.setAdapter(adapter);

    mDataBase = FirebaseDatabase.getInstance().getReference(USER_KEY);

    mDataBase.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(@NonNull DataSnapshot snapshot) {
        // очищаем список if (userList.size() > 0) userList.clear();
            for (DataSnapshot ds : snapshot.getChildren()) {
                User user = ds.getValue(User.class);
                userList.add(user);
            }
           // добавляем адаптеру метод adapter.notifyDataSetChanged();
        }

        @Override
        public void onCancelled(@NonNull DatabaseError error) {

        }
    });

    init();
    onClickShowAndHide();
}

private void init() {

    showComment = findViewById(R.id.btn_show_comment);
    hideComment = findViewById(R.id.btn_hide_comment);
    layout_comment = findViewById(R.id.layout_comment);
    layout_comment1 = findViewById(R.id.layout_comment1);
    edt_comment_name = findViewById(R.id.edt_comment_name);
    edt_comment = findViewById(R.id.comment);
}

public void onClickShowAndHide() {
    showComment.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            layout_comment.setVisibility(View.VISIBLE);
            showComment.setVisibility(View.INVISIBLE);
            hideComment.setVisibility(View.VISIBLE);
            layout_comment1.setVisibility(View.GONE);
        }
    });

    hideComment.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            layout_comment.setVisibility(View.GONE);
            showComment.setVisibility(View.VISIBLE);
            hideComment.setVisibility(View.INVISIBLE);
            layout_comment1.setVisibility(View.VISIBLE);
        }
    });
}

public void onClickSave(View view) {
    String id = mDataBase.getKey();
    String name = edt_comment_name.getText().toString();
    String comment = edt_comment.getText().toString();

    User user = new User(id, name, comment);

    if (name.equalsIgnoreCase("") || comment.equalsIgnoreCase("")) {
        Snackbar.make(view, R.string.checkout_fill_form, Snackbar.LENGTH_SHORT).show();
    } else {
        mDataBase.push().setValue(user);
        Toast.makeText(this, "Комментарий успешно добавлен", Toast.LENGTH_SHORT).show();
        layout_comment.setVisibility(View.GONE);
        layout_comment1.setVisibility(View.VISIBLE);
        showComment.setVisibility(View.VISIBLE);
        hideComment.setVisibility(View.INVISIBLE);
        edt_comment_name.setText("");
        edt_comment.setText("");
    }
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    switch (item.getItemId()) {
        case android.R.id.home:
            finish();
            return true;
        default:
            return super.onOptionsItemSelected(item);
    }
}

@Override
public void onConnected(@Nullable Bundle bundle) {

}

@Override
public void onConnectionSuspended(int i) {

}

}

решение прокомментировал в коде