Your argument is predicated on the assumption that if things change despite nothing changing in your ratings or activity, that means something is wrong. It doesn’t mean that at all. And it’s well documented that many factors outside of user control impact ratings, anyway. This is nothing new.
None of your information indicates or prove an algorithm change. Again, these are illogical conclusions.
For analogy’s sake, think of the logic this way: if I was getting a lot of business from an ad for three months and I stopped getting business this week despite the ad still being posted and despite nothing in my store changing, does that indicate or suggest that there is something wrong with the platform where the ad is posted or that they have put me at an unfair disadvantage? Certainly not. Because there are many factors and you can’t isolate them to prove your point.
You have no idea if the algorithm was always set to do all of these things. No idea at all. It’s simply not discernible from the information you’re presenting and it’s misleading to say otherwise.
The fact that many other sellers are experiencing the same thing also doesn’t mean that the algorithm has changed, either.