The problem was, that the results page maximum results count was set to 30. This meant that the plugin was limited to the first 30 matches, and after that, the out-of-stock function activated as well, removing even more results.
I have changed that number to 300, just like you have it on live results: https://i.imgur.com/ScX7L68.png
Now it should yield almost exactly the same results in reverse order when changing the ordering.
If you like my products, don't forget to rate them on codecanyon :)