Meta Ad Library API does not return any ad for some page and also not return same data as it shows on ads library

I have connected my application into Facebook Ad Library API using https calls.
It is working fine on some pages. but in some other pages it does not return all pages ads or in some it does not return any! but when you take a look at the page itself in the Facebook Ad Library Website. It is showing the page ads.
An example of this would be Hunger Games page which is at url https://www.facebook.com/ads/library/?active_status=all&ad_type=all&country=ALL&view_all_page_id=159746560708670&search_type=page&media_type=all and you can see that it is displaying more than 20 ads in the page but when you try to get its ads from the Ads Library API. it returns {"data":[]}