ExpandableList is hidden initially

Every time I start the activity with the ExpandableList it is hidden, so I have to press the shutdown button and restart it so it shows.

How do I resolve this?

My ExpandableList

<ExpandableListView
        android:id="@+id/lvExp"
        android:layout_width="match_parent"
        android:layout_height="450dp"
        android:layout_weight="1"/>

EDITION

All of my Layout

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@color/colorCorpo"
    android:orientation="vertical"
    tools:context="ham.org.br.nutricao.activity.CardapioActivity">

    <include
        android:id="@+id/toolbarCardapio"
        layout="@layout/toolbar" />
    <ExpandableListView
        android:id="@+id/lvExp"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_weight="1"
        />

    <Button
        android:id="@+id/btn_acao"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Button" />


</LinearLayout>

Activity

protected void onCreate(Bundle savedInstanceState) {
     super.onCreate(savedInstanceState);
     setContentView(R.layout.cardapio_activity);
     expListView = ( ExpandableListView ) findViewById( R.id.lvExp );
     toolbar = (Toolbar) findViewById( R.id.toolbarCardapio );
     toolbar.setTitle( "Cardápio" );
     setSupportActionBar( toolbar );

     listAdapter = new ExpandableListAdapter( this, listGrupo, listaItem );
     //setando list adapter
     expListView.setAdapter( listAdapter );
     int idTipoRef = bundle.getInt( "tipo" );
     String data   = bundle.getString( "data" );
     chamarTipoPratos( service, idTipoRef, data );

}

private void chamarTipoPratos( Service service, int idTipoRef, String data ){
        listGrupo = new ArrayList<String>();
        listaItem = new HashMap<String, List<String>>();
        listIngredientes = new HashMap<String, String>();
        listIngrediente = new ArrayList<String>();
        final Call<List<TipoPrato>> listTipoPratos = service.getlistTipoPratos("R", idTipoRef, data);
        listTipoPratos.enqueue( new Callback<List<TipoPrato>>() {
            @Override
            public void onResponse(Call<List<TipoPrato>> call, Response<List<TipoPrato>> response) {
           //     Log.i("onResponse TipoPratos",response.toString());

                if( response.isSuccessful() ){
                    List<TipoPrato> tipoPratos = response.body();
                    int i = 0;
                    for( TipoPrato tipoPrato : tipoPratos ){

                        //Log.i("Tipo", tipoPrato.getTipoprato());
                        ArrayList<Prato> listaPratos = tipoPrato.getPratoList();

                        listGrupo.add(tipoPrato.getTipoprato());
                        ArrayList<String> pratos = new ArrayList<String>();
                        ArrayList<String> ingredientes = new ArrayList<String>();

                        for ( Prato prato : listaPratos ){
                       //     Log.i("Pratos", prato.getPrato());
                            pratos.add( prato.getPrato() );
                            ingredientes.add( prato.getIngrediente() );
                            listIngredientes.put( prato.getPrato(), prato.getIngrediente() );
                        }

                        listaItem.put( listGrupo.get( i ), pratos );

                        i++;

                }

            }
            }

            @Override
            public void onFailure(Call<List<TipoPrato>> call, Throwable t) {
                Log.i("onFailure TipoPrato", t.getMessage());
            }
        });
    }