I have a Kindle Paperwhite and also use the Kindle app on my Android phone.
Recently, I've notice that when I convert an existing ebook to mobi (showing both for output), I keep getting a notification popping up in my Kindle saying that I can't sync to farthest page read and that I should close the book or put the Kindle to sleep before I can do this. I follow the instructions, but when I open the book again, it still won't sync.
On the Kindle app, it just says synced to furthest page, but it won't sync with
my Kindle. I have to set it to "old" on the output page for the sync to work properly.
Also, I've tried the conversion to awz3 & the same thing happens.