Yesterday, I noticed that i had 4.0 bat coins, then when i continued browsing amazon for example, i return to brave new tab page and i had been reduced to 3.7 bat coins.
I’ve noticed that other people have said the same thing, so i think its a bug.
I can also credit the other users who say that some adverts dont count towards the estimated BAT monthly reward, for example, it will take two or three ads for me to gain 0.1 of a BAT coin.