This question is about what AdSense isn't telling most of its publishers. Please don't regurgitate what they post on their help but rather tell us what they're not saying if you can.

Scenario: our website exists for nearly a decade. Currently we're at ~1 million daily pageviews. For some time we've had AdSense and noticed that the first months are much better than next ones. We dropped AdSense for some time, choosing user experience over revenue.

A few years later we decided to introduce it again, in least intrusive manner (ads on the bottom). Again, first months were really nice and then a small decline (say ~10-20%). Then, after about a year of us not changing the AdSense code and having roughly similar type of traffic and content (one cannot be 100% certain, right?), we saw a huge drop during the last days of September 2016. The drop was in CTR and thus revenues. Same kind/amount of traffic/content. We didn't make any changes in our sites in the few days before/after the drop was noticed.

Since then (3+ months) we've had various chats with AdSense support and nothing useful came out of those. Our CTR kept dropping and we're now at about 50% less than what the first months have brought.

Do what's going on 'behind the scenes' here? Do AdSense have some score for publishers that, when reduced, generates lesser ads? Seems like there's some preference towards newer publishers, is this so? Does it make sense to stop all AdSense serving every now and then?

AdSense support, if you care to know, were first telling us it could be an issue due to the beginning of a quarter. Proven wrong. Then they said it was about placement and suggested moving ads around and adding more ads (as they always do). Doesn't explain why a sudden drop would be experienced after about a year. Then they mentioned that their "arrow" feature isn't always shown due to invalid clicks and recommended that we move ads away from content on mobile. Did that and nothing improved. So far, useless.

This question is about what AdSense isn't telling most of its publishers. Please don't regurgitate what they post on their help but rather tell us what they're not saying if you can.

Scenario: our website exists for nearly a decade. Currently we're at ~1 million daily pageviews. For some time we've had AdSense and noticed that the first months are much better than next ones. We dropped AdSense for some time, choosing user experience over revenue.

A few years later we decided to introduce it again, in least intrusive manner (ads on the bottom). Again, first months were really nice and then a small decline (say ~10-20%). Then, after about a year of us not changing the AdSense code and having roughly similar type of traffic and content (one cannot be 100% certain, right?), we saw a huge drop during the last days of September 2016. The drop was in CTR and thus revenues. Same kind/amount of traffic/content. We didn't make any changes in our sites in the few days before/after the drop was noticed.

Since then (3+ months) we've had various chats with AdSense support and nothing useful came out of those. Our CTR kept dropping and we're now at about 50% less than what the first months have brought.

What's going on 'behind the scenes' here? Do AdSense have some score for publishers that, when reduced, generates lesser ads? Seems like there's some preference towards newer publishers, is this so? Does it make sense to stop all AdSense serving every now and then?

AdSense support, if you care to know, were first telling us it could be an issue due to the beginning of a quarter. Proven wrong. Then they said it was about placement and suggested moving ads around and adding more ads (as they always do). Doesn't explain why a sudden drop would be experienced after about a year. Then they mentioned that their "arrow" feature isn't always shown due to invalid clicks and recommended that we move ads away from content on mobile. Did that and nothing improved. So far, useless.