The Problem is Fixed when u Flush you'r Cache on the Browser you are using.
Mozilla Firefox
Click on Firefox at the top left of your browser, go to the History menu, select Clear Recent History and check all boxes. Under Time range to clear select Everything (except passwords, if desired) and click Clear Now.
Google Chrome
Expand the Wrench Icon in the upper right corner and select History and check all boxes. Under Clear data for this time period, select Everything(except passwords, if desired) and click Clear Browsing Data.
I have just tested it side by side, Firefox and Internet Explorer, on a Windows 10 LTSB machine that has never been connected to the Pihole before. Still the same thing.
Is it a server side cache perhaps ?
I had the same problem as Lupus (not a browser cache issue), installed sqlite3 to look at pihole-FTL.db and learned I had thousands of rows with timestamps around 2018-09-11 (in the future) in my pihole-FTL.db. (Clicking through the chart would've revealed the same thing. I realized that later.) Came back here to suggest what Mcat12 just suggested. It resolved my problem.