I've also noticed some really odd things this month and also contacted them.
But no one can give me an answer, nice as they are.
I track with kdp and novelrank. Novelrank has always been pretty accurate with kdp in the past. Maybe out a few percent but not much. My novelrank on one shows I have sales of 38 for one book but kdp shows 16. And for another book it shows 12 on novelrank but 20 in the graphs and 18 in the 'month to date.' Something is odd.
I'm going to email them again. Thanks for this. Aloha Meg Amor
I'd also like to add to this. I have over 20 books on Amazon and over the past four years have made steady, respectable sales, more than enough to earn a living (I generally write historical fiction). Then, at the start of May this year, the sales figures started to plunge. I have done all I can think of to boost them again, but by the end of August my income via Amazon was down to less than a third of what it was this time last year. Now the sales have dipped again and Amazon KDP have admitted - in response to my urgent query - that something is wrong with the final figures on my sales dashboard. They have repeatedly claimed to be working to fix the problem, but the plunging sales have continued for four days now and there is no sign of a solution. Amazon are my only income and this is extremely worrying and stressful.
Plunging sales are rarely a result of reporting issues and more often simply a result of less actual sales. By most reports July and August were bad months for the majority of authors/publishers so your sales drop in those months does follow the industry trend.
In my experience Amazon replies that they are investigating on all sale reporting queries yet more often than not they end up replying that there were no issues in the reporting. Hopefully you're the exception there and can recoup some of the lost sales.