App Open Ad is showing app content in place of advertisement

Question

My app was getting too high CTR for AppOpenAd which was around 35%-40%. So after looking for the issue I found that the AppOpen Ad is displaying the AppContent background in place of the advertisement. Below are the screenshots to demonstrate the exact issue.

So, in normal implementation as per the Google Admob Documentation. Below is the picture of what is exactly happening at many times. There is a comparison between the perfect display and problem happening display.

So, to work around I tried setting the background to the AdActivity with the following style and theme in Manifest file.

<style name="Theme.AppThemeNoActionBar.AdTheme" >
    <item name="android:background">@color/black</item>
    <item name="android:windowBackground">@color/black</item>
    <item name="android:windowExitAnimation">@null</item>
    <item name="android:windowEnterAnimation">@null</item>
</style>

And setting it into manifest file

<activity
        android:name="com.google.android.gms.ads.AdActivity"
        android:theme="@style/Theme.AppThemeNoActionBar.AdTheme"
        tools:replace="android:theme"/>

But still the issue remained same. Here the comparison picture.