Margin under ConstraintLayout guideline not appearing properly

I am trying to add some space underneath the Guideline for my constraint layout, but for some reason it doesn't appear to be applied. Does anyone know what is going on and how to apply 5dp of margin underneath the Guideline (for both portrait and landscape orientations)?

XML layout

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@color/lightgrey">
    <com.google.android.gms.maps.MapView
        xmlns:android="http://schemas.android.com/apk/res/android"
        android:id="@+id/map_townmap"
        android:name="com.google.android.gms.maps.SupportMapFragment"
        android:layout_width="0dp"
        android:layout_height="0dp"
        android:background="#09c"
        app:layout_constraintBottom_toBottomOf="@+id/guideline"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent"/>

    <android.support.constraint.Guideline
        android:id="@+id/guideline"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:orientation="horizontal"
        app:layout_constraintGuide_percent="0.9"/>

    <ImageView
        android:id="@+id/imageViewSun"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginBottom="5dp"
        android:src="@drawable/ic_sun_black"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toLeftOf="@+id/switch"
        app:layout_constraintTop_toBottomOf="@+id/guideline"
        />

    <Switch
        android:id="@+id/switch"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center_horizontal"
        android:layout_marginBottom="5dp"
        android:background="@android:color/transparent"
        android:theme="@android:style/Theme.Material.Light"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toRightOf="@+id/imageViewSun"
        app:layout_constraintRight_toLeftOf="@+id/imageViewMoon"
        app:layout_constraintTop_toBottomOf="@+id/guideline"/>

    <ImageView
        android:id="@+id/imageViewMoon"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:src="@drawable/ic_moon_black"
        android:layout_marginBottom="5dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toRightOf="@+id/switch"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/guideline"/>
</android.support.constraint.ConstraintLayout>

Portrait orientation

Portrait orientation (close-up)

Landscape orientation

Landscape orientation (close-up)