Days during which a user loses more reputation than they gain are shown as zero reputation on the graph on the user summary page. You can even see this on your own profile.
As you can see on the detailed reputation page, the serial upvoting occurred on march first, but the reversal didn't occur until march second at 3:00:
So the user gained reputation on Mar 1, which is clearly shown on the graph on the summary page. The user also lost all that reputation the next day, so the lost reputation would be shown on the next bar of the graph, if negative reputation were shown on the summary page graph. If you hover over that bar, you will see that even though there is no red bar pointing down, there is still a rep loss on that day: