This concerns the graph view on the reputation tab of your profile. (i.e. this thing)
In Chrome, the area selector doesn't show its bars.
Something similar appear to have been reported in 2011, but this is a completely different one. This isn't solved by returning to default zoom - in fact, the bars are somewhat visible in any zoom level except for the default one.
(Note the absence of the little spikes along the bottom row, or that specifically, they're white.)