Adsense Stats Year-Over-Year

A few weeks ago I started this current series of posts with an observation on my m-w.com domain, as documented in Chess Stats Year-Over-Year:-

In the past few months I've noticed a big drop in the number of daily visitors and I would like to know why.

Since it's always useful to get a confirmation of a trend from a second source, what does Google Adsense say? In the past I've noticed that the absolute numbers on my server log don't match the numbers in Adsense, but the trends should be similar, shouldn't they? Here's a chart showing Adsense stats from the first half of 2016 compared to the first half of 2017.

Although I've juggled the ad units over the 18 months covered -- as documented in the second post in this series, Site Stats and Adsense -- and although there is some noise in the 2017 portion of the chart due to the ads on my blogs, the totals are showing a definite upward trend year-over-year. That makes a downward trend on the server log and an upward trend on ad impressions.

This is not what I expected to see. How to explain this?