I mean, where is your actual traffic coming from - is it from the right country or countries? Coming in from Google or somewhere else? On the keywords you would expect it to come in on?
I think that these changes are tied to traffic quality. The example I use most often - if I have a site that is pretty tightly focused on Michigan, and I suddenly get a wave of users coming in from China - that's unusual. And if they click on ads, Google probably will think they're not like to be good for the advertisers, or likely to convert for them. So they will discount the clicks to the advertisers, and I'll take a hit on earnings. If it happens once in a while, well, it is what it is. It happens. If it happens over and over again, and in large amounts, then I could possibly have a problem. AdSense doesn't want to put the advertisers at risk, and they'll happily toss out a publisher, even if he hasn't done anything wrong, if he presents a risk to advertisers.
So you want to keep an eye on your traffic. An occasional anomaly is not a big deal, but sustained anomalies - if I had, say, three months in a row where they took back a significant amount of money when it was finalized - then I'd probably be temporarily turning off AdSense till I figured out what was going on.
That's my strategy, anyway.