Goodreads, the book review site, is about thirteen years old and has had systemic troll problem for most of those years. Matters had reached crisis proportions way back in 2012 (see https://en.wikipedia.org/wiki/Goodreads#Competition_and_review_fairness ). Some of the issues arose not from trolling as such but from the inevitable conflict between authors and readers when assessing the content of books (e.g. see https://www.salon.com/2013/10/23/how_amazon_and_goodreads_could_lose_their_best_readers/ )
You would think that over that period of time Goodreads would have developed some robust systems and processes for dealing with trolls and abuse. After all, you would imagine that a review site descending into a slime pit would inevitably lead to both authors and readers looking elsewhere. That does not seem to be the case.
Notably, author Patrick S Tomlinson is currently being targetted by a sustained cyberstalking attack on Goodreads. Multiple fake accounts are leaving insulting reviews of a book of his that has not yet been published (not even as an ARC). The fake accounts have been quite blatantly using fake names and identities, including a fake account pretending to be Otis Chandler one of the founders of Goodreads.
Another author targetted for harassment and identity theft is former SFWA President Cat Rambo:
With little moderation and few tools available for reporting fake accounts or harassment, a coordinated troll attack can be very difficult to stifle even when the reviews are absurdly and blatantly false.
ETA for additional context: