I would call it the "core update sandbox" and I've also observe it, but my theory is that the algos are in "harsh" mode: many sites with this kind of unbalanced content (classic service site with 5 pages for services and 1500 blog posts talking about services that they don't even work), are subject to some degree of shittyness.
This is why I said this:
Try to identify if whitehat site with 100% genuine content is, on a scale of 1 to 10, probably a 5 on quality. I must say 100% of my super tier sites are never touched by algo updates.
Why? Because its not only genuine content but killer content (and also we have to admit that generally killer content is under optimized, for obvious reasons)
In fact, the site that is still penalized and I mentioned above that has not recovered is a YMYL site that used to have killer content, but at some point, with my brilliant mind, I decided to overoptimize it.
For example, one of the pages, could be technically analyzing the evolution of the Hemorrhoids and the article was citing like multiple papers and all that stuff.
Then, at some point I decided to insert H2 like:
View attachment 231712
And structure the content on that way.
And despite I noticed a great upturn, the page over the time has not done anything but plummet. First I started thinking that it was a YMYL issue, but since Dr. F. L. ""joined"" our team, I could say that YMYL was not a thing, but probably the over optimization that converted many killer aticles in so-so stuffed s**t that could be written by any writer in any marketplace. Why I did that? I felt that the page was 100% stuck and I wanted to squeeze it a little more. And since I restructured the site in many other ways, a rollback no is not viable (and completely unexpected how results will behave with such idea).
I feel that there will be two branches on how Google will be (and is) treating sites with all this updates: the mass content creators (black hatters, trying to deceive the algo with many techniques) and the mega-spezialized (real EAT people that write of what they really know), and all the people in the middle will be out of the game. In fact this is the paradox of the Artificial Intelligence and automation: most of the jobs "in the middle of the process chain" will be destroyed because automatism will be slowly replacing them. And I think that since BERT, this starts to become a reality in this industry.
This said, I think this is very unlikely to be the intention, since Google also make business from the ad network, not only Google Ads. I feel it's farfetched that they could be willing to kill their ad network to favor real ad spenders, and probably this is one of the reasons on why many newspapers are unifying their assets into one huge subdomained site (I hope that Google solves this anytime soon), because it feels that Google is putting too much importance into Domain page-rank-level, rather than URL page-rank-level, meaning that the sites that are always benefited from this "core-update-sandbox" are ALWAYS the subniche subdomains from huge domains.