Caliber doesn't store the latest Kobo ebooks

Hy,
1) I open calibre and connect Kobo Clara 2E
2) There are all the book and also the book on the device
3) I send some ebook on the device
4) Now Calibre show that these books are in the device
5) Restart Calibre
6) Now The latest books sent are no longer in the device, the last books resulting in the device are those of the point 2
Why ? And is there a solution ?
Thanks
pacmo