One of the more serious issues with the latest firmware version hasn't been adressed here yet: the "Invalid ASIN" error message, resulting in an endless loop. For details, see
https://www.amazonforum.com/s/questi...s-invalid-asin
I encountered the problem myself with my (many) sideloaded books and I can confirm that the workaround (opening books via the three dot menu once) does work for me (Kindle Paperwhite SE, 11. Gen.). It's a shame nevertheless...