Everyone has had reviews disappear. The fact that you knew the reader had posted a review suggests you knew the reader. Amazon will take down reviews it suspects of being from friends & family.
Or did you just notice the review, think Oh boy! and then have it disappear again? This happens. Sometimes the reviewer changes his/her mind. Sometimes a reviewer may have taken money for reviews, then have all their reviews taken down by Amazon, including perfectly innocuous ones. Sometimes reviews mysteriously disappear and then return just as mysteriously.
Basically it's not worth worrying about, although I know, it's hard not to. There's really nothing to be done. Good luck!
I wonder how Amazon makes the assumption that a review is from friends or family?
The first review of my new self help book is a five star rave, but it's from someone I've never met.
He's the brother of an acquaintance, so likely saw a facebook discussion.
I admit, if I didn't know better, I would assume it was from a friend being sweet. Oh well. Whatever.
Joseph M Erhardt wrote:
"Any A.I. smart enough to pass a Turing test is smart enough to know to fail it."
Recently, I read Infinity Born by Douglas E. Richards. Way too much info-dumping and pedantry, but the premise was interesting, so I finished the book. It goes beyond AI, to ASI (artificial superintelligence). The future is now