and the conclusion ...

[loukasenna]

Amazon explained the de-rankings as "a ham-fisted error" and books are getting relisted.
 
Still, this by Richard Eoin Nash (via copperbadge) is spot-on:

[...] it is always the GLBTQ books, the queer books, the non-normative books that get caught in the glitches, the ham-fisted errors.