AdMob Ad Serving has been Limited due to Invalid Activity

• Google is working on their own terms since they have monopoly in the market. It's really difficult to say if any kind of traffic they don't like but we have Proprietary Fraud Detection System to ensure traffic (installs) are from real users / devices only.
• Since Google did not transparently provided any clear explanation as expected since they often do one-sided decision and the worst thing is these decisions are automated.
• However, we did some research and found that usually ad serving limit typically impacts publishers for less than 30 days, it may take longer in some cases.
• Limited ad serving applies to AdMob Network only and doesn’t affect third-party mediation, house ads, and direct sold campaigns. - Have you setup third-party mediation?
• It is highly recommended not to rely solely on Google since they have monopoly in the market, they often do one-sided decision and the worst thing is these decisions are automated.

Some useful information, might be helpful:

• Invalid traffic includes any clicks or impressions that may artificially inflate an advertiser's costs or a publisher's earnings. Invalid traffic covers intentionally fraudulent traffic as well as accidental clicks.

Invalid traffic includes, but is not limited to:

• Clicks or impressions generated by publishers clicking on their own live ads
• Repeated ad clicks or impressions generated by one or more users
• Publishers encouraging clicks on their ads (examples may include: any language encouraging users to click on ads; ad implementations that may cause a high volume of accidental clicks; etc.)
• Automated clicking tools or traffic sources, robots, or other deceptive software