I just found out the reputation tab on the profile page has this graph feature. I looked at the small graph and saw a high peak in September. I tried to view it by clicking and dragging, but was confronted with a huge peak and no info on what caused it:
Now this suggested either a huge loss to neutralize the peak (very unlikely), or something wrong with the graph feature. The following picture seems to confirm the second option:
That is a net gain of +29 rep. However too big the peak in the graph may be, it still is justified. And there is no huge loss to neutralize it. So is there a bug in the graph feature?
Update
As comments pointed out, it seems I got two different Sep 24's mixed up. The rep tab picture shows Sep 24 2015, the peak is from 2014. Here is the peak in the rep by time tab:
Seems the commenter got the peak wrong: 76, not 79 :). Anyways, now the size of the peak in the graph is decidedly appropriate. And the "no net gain" sounds even more absurd.