If you make a search on Commons for nadja hirsch (link: https://commons.wikimedia.org/w/index.php?search=nadja+hirsch&title=Special:Search&go=Go) you will get the following result:
It looks like the update for this category (currently in two indexes) hasn't gone through it's update. We'll try to update this manually, but in general, this process can take up to two weeks to completely regenerate.
Cause and effect is not the same - this single example is fixed, but the fact that such an update may cause the same result to appear twice, seems like a bad underlying cause/problem.
the problem is simply moving results between indexes, while the move is underway there will be duplicates. There is no nice way to move 10's of millions of documents atomically.