Happened to me when I saw a book on the US site, I wasn’t able to see all reviews, but there was a button to sort-of “apply” to get approved for seeing all of them.
It took five days, then I got this email.
Interestingly, they’re not doing this on the European site, you can still see all reviews there.
I’m in the US. Not once have I seen or even heard of this happening before.
I’m guessing it’s something only being done to the EU when trying to look at Amazon from other countries, or just when looking at other Amazon’s outside your own country.