I've spotted two potential problems with the reputation tab, I hope both are documented on the image below:
First of all, there seems to be a off-by-one error. If september 24 is selected (in gray), The list underneath it shows +20 (which was, as the tooltip advices), the reputation of the day before. This behavior is spotted on all days. Perhaps it depends on the user's time zone. For me this is Central European Time (CET) (mentioning this for debugging purposes).
Furthermore as the image shows, removed posts are shown as well. This however results in the fact that the reputation cap is no longer taken into account. The total reputation for that day is
480, but this is partly realized with a post that was later removed. This is perhaps more a discussion on whether to take the reputation cap into account.