Admob account suspended due to "invalid activity on the AdSense ads hosted on your website"

From googles support pages:

Invalid click activity consists of any clicks or impressions that may artificially inflate an advertiser's costs or a publisher's earnings, and for which we decide not to charge the advertiser. This includes, but is not limited to, clicks or impressions generated by a publisher clicking his own ads, a publisher encouraging clicks on his ads, automated clicking tools or traffic sources, robots or other deceptive software.

Basically, they want genuine user interest. Most of the generated revenue from your app may have been from one person (intentional or not) which has lead them to believe that the clicks were fake. Google uses very sophisticated Artificial Intelligence program to track user mouse pointer location on the page and using the mouse pointer behavior it decides whether it’s a legit or fake click. Sometimes the app or website owner will click the links themselves. This 30 day ban is a cooling off period.

Some common causes of bans regarding invalid clicks:

• Don't click your own ads (see above)
• Don't tell your friends to click on your ads
• A page impression can still be counted towards revenue. Don't let friends browse your ad hosting pages on your account (this will be viewed as YOU)
• Don't use copyrighted content
• Don’t post or host malicious content (hacking etc...)
• Don’t use pornographic materials on your site.
• Don’t use any other ad service on your website while using AdSense
• Don’t put more than 3 ads on any page.

Google recommends that to prevent invalid activity, that your ad implementation adheres to its policies. Here is a full list of Google AdSense policies .

Google also has additional guidelines on how invalid activity can be prevented. https://support.google.com/adsense/answer/1112983

Finally:

Get involved with your Google Analytics to see where your users are coming from, and if you truly feel that you have been incorrectly banned, you can appeal here - Invalid Activity Appeal.

Forget Admob and use Facebook audience network ads. its great ads network for mobile ads And you will get 30% more revenue than Adsense.