Help to Understand "Google AdMob ad serving has been disabled to your application"

Today I received below email from admob.
its about disabling ads on one of my app.
Now I am using interstitial on load of app and banner on the top left corner of app,its admob,inmobi and amazon ads via admob mediation.

I am not changing behavior of ads nor I am covering any portion of ad inside app.

If anyone has faced such issue before or know more about it,
I look forward for your kind guidance so that I can change the app and resolve the issue.

Thank you
------------Original email of admob I received ---------------------
This email is to alert you that one of your applications is not currently in compliance with our AdMob program policies and as a result, ad serving has been disabled to your application.

Issue ID#: 1222869

Action required: Check all other remaining applications in your account for compliance.

Current account status: Active

Violation explanation

ADS AND CONTENT OVERLAP: As stated in our program policies, publishers are not permitted to alter the behavior of AdMob ads in any way. This includes placing ads so that they cover any part of the application content or parts of an application covering any portion of the ads. If your app has drop-down menus they are not permitted to cover AdMob ads.