Why is Google Ads crashing android app only on release version?

I am building an Android app with Android Studio with Google Ads. The app seems to work well when I build it locally with test ads, but once I generate a released build, Google Ads throws an error in the middle of the app.

Any insight is appreciated, thank you!

Stack trace from production app

CountDownActivity.java

public class CountDownActivity extends AppCompatActivity {
   private AdView mBannedAdView;
   ...
   @Override
   protected void onCreate(Bundle savedInstanceState) {
      mBannerAdview = findViewById(R.id.adView_count_down);
      if (mBannerAdview != null) {
         mBannerAdview.loadAd(adRequest);
      }
   }
}

activity_count_down.xml

<RelativeLayout>
    ...
    <ImageView
        android:id="@+id/answerImage"
        android:layout_width="300dp"
        android:layout_height="300dp"
        android:layout_centerHorizontal="true"
        android:layout_centerVertical="true"
        android:adjustViewBounds="true"
        android:visibility="invisible"/>

    <com.google.android.gms.ads.AdView
        android:id="@+id/adView_question"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerHorizontal="true"
        android:layout_alignParentTop="false"
        android:layout_alignParentBottom="true"
        ads:adSize="BANNER"
        ads:adUnitId="ca-app-pub-<AD-ID-HERE>"
        />
</RelativeLayout>