In early 2017, this kind of thing happened. Got a remedy for a while, then by mid 2017, Amazon did it again of not allowing registration from the device. You can read it here:
https://www.mobileread.com/forums/sh...d.php?t=283281
The problem got a brief remedy because some of mobileread's users emailed Jeff Bezos with a hard message. From the thread, Amazon really can exercise their authority to do what they want to do with our Kindle device. So there is no guarantee that once they can get a seemingly "legit" issue for the later Gen they will not again exercise their authority.