Elevation não está exibindo a sombra

Apesar de definir o elevation nos RelativeLayouts, a sombra não aparece no componente. O que pode ser?

Segue abaixo meu layout:

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:id="@+id/activity_cadastro_produto"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#fff"
    android:clipToPadding="false"
    tools:context=".MainActivity">


    <ScrollView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_alignParentTop="true"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true">
        <LinearLayout
            android:orientation="vertical"
            android:layout_width="match_parent"
            android:layout_height="wrap_content" >

            <LinearLayout
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:layout_marginLeft="15dp"
                android:layout_marginRight="15dp"
                android:layout_marginTop="15dp"
                android:orientation="vertical">

                <ImageView
                    android:id="@+id/imageView"
                    android:layout_width="180dp"
                    android:layout_height="70dp"
                    android:layout_marginLeft="-13dp"
                    android:layout_weight="1"
                    app:srcCompat="@drawable/logo" />

                <TextView
                    android:id="@+id/txtwelcome"
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:layout_marginBottom="10dp"
                    android:layout_marginTop="10dp"
                    android:layout_weight="1"
                    android:text="OLÁ FULANO!"
                    android:textColor="@android:color/holo_red_dark"
                    android:textSize="16sp" />

                <TextView
                    android:id="@+id/textView2"
                    android:layout_width="match_parent"
                    android:layout_height="wrap_content"
                    android:layout_weight="1"
                    android:text="Nossos serviços, disponíveis para você:"
                    android:textSize="13sp" />

            </LinearLayout>


            <LinearLayout
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:orientation="vertical"
                android:layout_marginTop="15dp"
                android:clipToPadding="false">

                <LinearLayout
                    android:layout_width="match_parent"
                    android:layout_height="match_parent"
                    android:layout_weight="5"
                    android:orientation="horizontal"
                    android:weightSum="10">

                    <RelativeLayout
                        android:layout_width="match_parent"
                        android:layout_height="80dp"
                        android:layout_marginLeft="3dp"
                        android:layout_marginRight="3dp"
                        android:layout_marginTop="3dp"
                        android:layout_weight="5"
                        android:background="@drawable/main_rounded"
                        android:elevation="3dp">


                    </RelativeLayout>

                    <RelativeLayout
                        android:layout_width="match_parent"
                        android:layout_height="80dp"
                        android:layout_marginLeft="3dp"
                        android:layout_marginRight="3dp"
                        android:layout_marginTop="3dp"
                        android:layout_weight="5"
                        android:background="@drawable/main_rounded"
                        android:elevation="3dp">


                    </RelativeLayout>


                </LinearLayout>

                <LinearLayout
                    android:layout_width="match_parent"
                    android:layout_height="match_parent"
                    android:layout_marginBottom="10dp"
                    android:layout_marginTop="10dp"
                    android:orientation="horizontal"
                    android:weightSum="10">

                    <RelativeLayout
                        android:layout_width="match_parent"
                        android:layout_height="match_parent"
                        android:layout_weight="5">

                        <RelativeLayout
                            android:layout_width="match_parent"
                            android:layout_height="160dp"
                            android:layout_marginLeft="3dp"
                            android:layout_marginRight="3dp"
                            android:layout_marginTop="3dp"
                            android:layout_weight="5"
                            android:background="@drawable/main_rounded"
                            android:elevation="3dp">


                        </RelativeLayout>
                    </RelativeLayout>

                    <LinearLayout
                        android:layout_width="match_parent"
                        android:layout_height="match_parent"
                        android:layout_weight="5"
                        android:orientation="vertical">

                        <RelativeLayout
                            android:layout_width="match_parent"
                            android:layout_height="match_parent"
                            android:layout_marginBottom="5dp"
                            android:layout_marginLeft="3dp"
                            android:layout_marginRight="3dp"
                            android:layout_marginTop="3dp"
                            android:layout_weight="5"
                            android:background="@drawable/main_rounded"
                            android:elevation="3dp">


                        </RelativeLayout>

                        <RelativeLayout
                            android:layout_width="match_parent"
                            android:layout_height="match_parent"
                            android:layout_marginLeft="3dp"
                            android:layout_marginRight="3dp"
                            android:layout_marginTop="8dp"
                            android:layout_weight="5"
                            android:background="@drawable/main_rounded"
                            android:elevation="3dp">


                        </RelativeLayout>
                    </LinearLayout>
                </LinearLayout>

                <LinearLayout
                    android:layout_width="match_parent"
                    android:layout_height="match_parent"
                    android:layout_weight="5"
                    android:orientation="horizontal"
                    android:weightSum="10">

                    <RelativeLayout
                        android:layout_width="match_parent"
                        android:layout_height="80dp"
                        android:layout_marginLeft="3dp"
                        android:layout_marginRight="3dp"
                        android:layout_marginTop="3dp"
                        android:layout_weight="5"
                        android:background="@drawable/main_rounded"
                        android:elevation="3dp">


                    </RelativeLayout>

                    <RelativeLayout
                        android:layout_width="match_parent"
                        android:layout_height="80dp"
                        android:layout_marginLeft="3dp"
                        android:layout_marginRight="3dp"
                        android:layout_marginTop="3dp"
                        android:layout_weight="5"
                        android:background="@drawable/main_rounded"
                        android:elevation="3dp">


                    </RelativeLayout>


                </LinearLayout>
            </LinearLayout>

        </LinearLayout>
    </ScrollView>
</RelativeLayout>

Eu desenhei o componente com borda arredondada, vou colocar aqui também pra ficar facil replicar:

<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">
   <item>
        <shape android:shape="rectangle">
            <corners android:radius="3dp"/>
            <solid android:color="@android:color/transparent"/>
            <stroke android:color="#696969" android:width="1dp"></stroke>
        </shape>
    </item>
</selector>

android:clipToPadding="false"