If you saw your AdSense CPCs decline starting on Sunday, August 5, you are not alone. Google advertisers blacklisted after exploiting AdSense, driving down CPCs. Google has confirmed they have blacklisted some ad buyers after they exploited their ad system, which resulted in AdSense publishers noticing declines in their CPCs over the past few days. Credits - http://searchengineland.com/google-advertisers-blacklisted-exploiting-adsense-driving-cpcs-280475 https://www.seroundtable.com/cpc-drops-google-adsense-publishers-24272.html
You realize that $ would have been flagged as bad income eventually and subtracted from your balance. I had considerably higher invalid traffic this month, so that was probably this.
Here are the Details On The Google AdSense/Ad Buyer Exploit. https://www.seroundtable.com/details-google-adsense-ad-buyer-exploit-24298.html