This is fascinating. I haven't really kept up with SEO for years, but was recently helping an academic publisher setup their web presence and ran into exactly this issue: Google was/is refusing to index the actual journal articles on the new site and they were moved into this liminal "Crawled, not indexed" state before vanishing entirely. Comically, it's now easier to get your content indexed and served with a visible link by ChatGPT than it is Google...