I was looking at some recently earned reputation here on Meta and noticed that the activity log seemed to be duplicating some events within rollups.
In this screenshot, 25 + 5 = 30, everything seems to be in order.
When we expand the rollup of 5 events, 6 events get displayed. It looks like the most recent upvote gets displayed twice, both at the top and in the rollup.
I almost thought I was losing points somehow before I noticed that it was likely that the latest was duplicated on the display.