I know there has been talk over the years about ceilings in adsense earning, and conspiracy theory stuff, so I' m just going to share an observation.
One of two things happens to my earnings/RPM during the last 4-5 days of each month. Consistent.
If my earning for the current month are higher than my usual, even by let's say 50-100 dollars, then the last few days of the month earning drop to almost nothing.
If on the other hand, my earnings for the current month are below average, then the earning during the last few days spikes. So rather than an average RPM of let's say $3.00, it might go up to $16.00 just for those few days.
So, in the end, I earn just about the same each month, although progressively lower. This is on sites that have been around for years, once made 3k a month and now sit at lower to mid $000.
So what could explain this? What mechanism?
Practically the answer isn't actionable, but I am curious.