E-books don't appear on my Kobo Mini after I have downloaded them from my computer.

I've downloaded some e-books from my library online. They appear in my Adobe Digital Editions on my computer and appear to successfully transfer to my Kobo Mini device, but when I eject my device and look at what books I have on my Kobo Mini, none of the new books are there. I don't understand because until now I have been downloading library books to my device without any problems. I tried unauthorising and then reauthorising my computer but that made no difference.

Any advice would be greatly appreciated!