Books and authors who write work characterized as erotica or as LGBTQ have had their ranking stripped from their books. Why is this an issue? Because then they don't show up on best-seller lists, suggested reading lists and other things. See this post here from dearauthor.com for more info on how it works and why it's a big deal.
Now, I have no problem if someone wants to use an Adult Content filter on their own searches but I disagree entirely with someone else imposing their standards on what I read. I also object to the blatant favourtism given an author like Laurell K. Hamilton whose Merry Gentry books, as much as I enjoyed them, are essentially excuses for smut: het, gay and group smut plus torture and blood. Yet her books get to keep their ranking. Why? Probably because she sells lots and makes them lots of money. Same with Anne Rice.
You can contact Amazon directly to tell them of your concerns (if you are) by emailing them from this site: https://www.amazon.com/gp/help/contact-us/general-questions.html?ie=UTF8&type=email You will need to register to use it.
There is an online petition, mentioned in the dearauthor.com post, but here's a direct link to it: thepetitionsite.com. I hope you'll take a moment to fill it in and to spread the word.
[Edit]: There is the possibility that this is a deliberate campaign by a group(s) taking advantage of the complaint process. Read the post by tehdely here. I agree it's possible--libraries get this all the time, but it's still Amazon's responsibility to legitimately assess each content complaint. They could also add an optional Adult Content filter to their site, like Google.search, or Veoh or even LiveJournal.