This is a known quirk of sideloading Kepub, which I explained in this thread recently:
https://www.mobileread.com/forums/sh...d.php?t=312152
I suspect you do not have this problem with epub books, and would ask that you verify that statement. (Long press on the book cover, select "View Details" from the menu, Press "Details" tab, File Format: will be either "EPUB" or "KOBO EPUB"