I do not know the details, but many of my writing friends that use Kindle and Publish through Amazon had noted that their books aren't showing up on the US store Page.
I actually have no idea if this is just because a lot of them are Erotica authors, if it's because they are or aren't in Kindle Unlimited (I am in Kindle Unlimited) or if it is simply Amazon changing how books are put on the store and it's taking longer.
As someone who writes from the US I haven't experienced any differences yet. While I get a majority of my sales from the US, I get reads from all over the world.
I haven't really noticed a difference yet, but I'll keep an eye out.
More importantly, regardless of the reason, Amazon not really giving writers a heads up is rather poor.
Once again I want to think this isn't them trying to push sales or anything like that, but the lack of information always makes people think the worse.
I'll keep gathering information and talking to people whenever I can.
This issue only exists on the US Amazon store.
It is only affecting writers based outside of the US.
It is affecting all genres - erotica, romance, paranormal, fantasy, horror, etc.
It doesn't matter whether you are enrolled in Kindle Unlimited or not.
It is only affecting Kindle books.
It seems to be affecting all books published after the 25th March 2018.
I've spoke to Amazon a bit today and most of their reps aren't unsure of the problem (or don't believe it exists). If you search for my pen name on the US store, though, you'll see that only 9 books show up when I have 25 released. The rest can't be found without a direct link. The latest Amazon rep said they'd get back to me in 3-5 days...