If a post is deleted as spam or offensive, the user incurs a 100-rep penalty. But SE made the conscious decision to not call that out on the reputation tab; if you go to the page of a user who's hit this penalty, you won't see those "-100" events in the history. The big rep number on the profile will be correct (which is important for knowing about privileges), so you'd only notice the difference if you went through the history and added everything up -- probably not something that happens often.
So these rep penalties would be invisible to most viewers, but for one thing:
(You'll need to get your own test case to verify this behavior; I'm not going to call out specific users.)
How is the current rep both 404 and a smidge over 500 at the same time? There's only one way I know for that to happen (and I know it happened here).
You might think that, theoretically, answers that the user downvoted could account for the difference, because those too are not shown in rep history. But the -1 rep for downvoting answers is reflected in the graph, even if an audit of the rep history would come up with a different number.
If we don't want to call out these events in the rep history, should we also do something about this graph to avoid broadcasting what happened in the summary?