What is the bug ?
Discussion
Mine all coins (you will receive 20 sats), wait for advertisement, close the app and open again. All your mine coins will be reset and you can mine them again. Therefore you will receive 20 sats more. 
What is the bug ?
Mine all coins (you will receive 20 sats), wait for advertisement, close the app and open again. All your mine coins will be reset and you can mine them again. Therefore you will receive 20 sats more.