I get one of these each month, and it's usually right around the beginning of the month. It has NO link to the stats that I can see - it's as if accounting is playing "catch-up" on something. Every month, right as rain. It's nothing I'm doing right or wrong, in terms of content.

I get the same sort of thing on my blog, though, too, so I suspect it won't tie in to revenue, and is rather linked to external web crawler bots' "views". They tend to run on a schedule. I've quit worrying about it. It IS odd, though.