Yes it's because the PRIVATE folder is in the root and so is the KN24PRG.DAT.
You're right it is possible for the operating system to be a problem, I've had problems before too but not so much with file transfer, well I can't remember a file transfer issue. More likely when it is unzipping. If the format is done in the keyboard then the file system should be fine on the card.
The only way I can help further is to try it on the same model. We'll try that beginning of Feb and will try the file transfer with Windows 10, Windows 7 and XP. It will be interesting to find the correct procedure.
I had a similar problem on my KN7000. In the end I found that I had to press and hold the buttons very, very hard. Maybe I had some bad contact on one of the buttons. I also seem to remember that I used google translate from German to English then and there was some small thing I missed from the translation. AND I remember that one of my floppy disks had a problem and I had to re-write it on a new floppy disk. Because KN7000 does the upgrade from floppy.
I'm stumped right now