I have the same experience. I just posted my experience and requested some help, but it appears your experience is exactly what I now have.

Hello, Thanks for your prompt reply -- I had actually posted something identical a few hours ago, and got some replies which were very helpful. I commented on this one just to confirm that I am experiencing the same. Based on the reply to my post, I am convinced -- though I will wait for the actual experience to confirm -- that the root cauase for my being unable to get a weekly traffic monitor report is that I hd enabled the C4000 A20 router to reboot daily. Therefore the log (which I assume contains the traffic data as well) was erased every 24 hours and I could only get one day's data. Therefore I went back to my router and disabled the "reboot daily" setting. I am waiting about a week to see if this turns out as expected. Many thanks for your response.

My sincerest thanks for your timely assistance. After waiting more than a week to be absolutely sure, I confirm that I am getting a full week's data as long as I do not reboot the router during the entire period (in my case 1 week) for which traffic data is being collected. So I had to turn OFF the router reboot schedule, and this fixed the problem. Thanks again!