As an Apple employee (not in any role related to the app store), and satisfied user of Happy Scale, I'm sorry to hear about the ranking loss.<p>On the other hand, it's in the nature of machine learning systems such as search that sometimes, a simple update of the underlying model can lead to drastic changes in search results (say, for argument's sake, that there has been a recent influx of apps using the word "tracker", which could lead to the word being considered essentially noise).<p>This can happen without any "bug" in the underlying system, even less a sinister agenda to undermine any developer or help another one. So while these possibilities can and should be investigated, ultimately search results will sometimes change.