Issue with furthest page read on Kindle ebook

[Hollow Man]

I switch between my physical Kindle and the Kindle app on my iPhone. I'm having an issue that ever since I went to the endnotes of a book (Infinite Jest; one of the endnote popups didn't work properly, so I was forced to go to the end of the book) it now thinks the endnotes section is the furthest page read.

I went to Amazon's site, found the book in my list of purchases, and initiated the "clear furthest page read" option. This worked the first time. But when I went to the endnotes again, then tried to clear the furthest page again...now it always wants to go to the end of the book whenever I choose "sync to furthest page read" from the Kindle of Kindle app.

Note: both the app and Kindle properly sync to the last page read (if I read further on one device, then open on the other). It's only if I choose "sync to furthest page read" that it tries to jump to the end of the book.

I've tried "clear furthest page read" more times than I can count, marking the book read then unread, going to beginning of the book, deleting the book from the Kindle and phone...nothing works.

Ideas? Thanks!