App crashes when I return to map activity containing ad banner?

As qtmfld pointed out, your error is most likely happening in the RenderThread. My educated guess is that it has to do with your banner ad drawing on top of the map fragment.

There are known drawing issues when using hardcoded fragment elements in xml layouts, especially when using fragment transactions. Therefor, it is possible that SupportFragmentManager is somehow trying to draw over the banner ad when recreating the fragments state, which is causing the crash.

Apart from that, it is against Google's ad policies, to use banner ads above components, that the user interacts with.

To confirm this you can try changing your layout constraints so, that the banner ad doesn't overlay the maps fragment:

 <fragment xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:map="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/map"
    android:name="com.google.android.gms.maps.SupportMapFragment"
    android:layout_width="match_parent"
    android:layout_height="0dp"
    app:layout_constraintTop_toTopOf="parent"
    app:layout_constraintBottom_toTopOf="@id/banner_container"
    tools:context=".MapsActivity" />

You Mixed up some things!

Have a look at the Facebook Documentation under: initialize-the-audience-network-sdk

You can see that they call AudienceNetworkAds.initialize(this); in the Application class and not in the Activity.

Create a Class like in the documentation:

public class YourApplication extends Application {

    @Override
    public void onCreate() {
        super.onCreate();
        // Initialize the Audience Network SDK
        AudienceNetworkAds.initialize(this);       
    }

}

The next Step is to add the class with android:name=".YourApplication" in the Manifest file, like in the example:

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="it.rieger.com.myapplication">
<application
    android:allowBackup="true"
    android:icon="@mipmap/ic_launcher"
    android:label="@string/app_name"
    android:roundIcon="@mipmap/ic_launcher_round"
    android:supportsRtl="true"
    android:name=".YourApplication"
    android:theme="@style/AppTheme">
    <activity android:name=".MainActivity">
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>
</application>

This tells Android where he can find your implementation of the Application class.

Then remove the AudienceNetworkAds.initialize(this); line from your onCreate() Method in the class MapsActivity.

Now everything should work well.

Why does the exception show up?

Have a look at the Activity Lifecycle.

onCreate() can be called by the system at every startup of your Activity and not only onResume() or onStart().

What happens is that the emulator call onCreate() when you open the Activity for the second time over the onCreate() method. Which leads to a second call of AudienceNetworkAds.initialize(this); which causes the error.

Another hint

Don't forget to implement the onDestroy() method like:

@Override
protected void onDestroy() {
    if (adView != null) {
        adView.destroy();
    }
    super.onDestroy();
}

Please check if you are using HAXM based emulator and check if it also happens in real devices.

You can also try Google Maps Android SDK v.3.1.0 BETA and see if the bug still exists.

In the Logcat message:

A/libc: Fatal signal 11 (SIGSEGV), code 1 (SEGV_MAPERR), fault addr 0x0 in tid 14320 (RenderThread), pid 14265

• A/libc shows that the priority is A (Assert) and the tag is libc (bionic).
• The message is Fatal signal 11 (SIGSEGV), which means that your app terminates itself, receiving a signal of segmentation violation.
• code 1 (SEGV_MAPERR), fault addr 0x0 details that libc failed to read or write memory address 0x0 (null pointer), as explained in this answer.
• The rest in tid 14320 (RenderThread), pid 14265 shows that this crash took place in thread 14320 (RenderThread) of process 14265.

RenderThread indicates that this might be due to hardware acceleration.

To turn off the acceleration, add an attribute

android:hardwareAccelerated="false"

to one of these elements in AndroidManifest.xml.

• The whole <application />.
• The <activity /> that crashes.

I think it's worth a try.