Books appear on old Kindle but not new one.

Hi All,

I'm having an issue where books that I transfer from Calibre to an older kindle(my wifes') do so fine without any issues and show up under books.

However when I try to transfer them to my kindle, the one with the basic touchscreen, the only way I can find them is by doing a search on the device. When I do the icon next to it shows as a book and if I select this it will open up normally, but when I attempt to find it under books its not there.

Obviously it is saving to the Kindle but is putting it somewhere not visible.

I don't understand why it works ok on one Kindle but not the other. I have even tried resetting it.

The transfer is done via usb with the Kindle plugged in. I am using MOBI for both devices.

Any help or assistance appreciated.

Thanks