Side-loaded KEPUB files show up on my Kobo, but not on Calibre's Device page?

[hengyu]

I convert my books to KEPUB using the KEPUB output plugin, I hit send, and when I eject, the book shows up in my Kobo just fine, but I don't see it on my Device Library or the green "On Device" tick.

The files are there on the Kobo's drive on Explorer.

I'm very confused as to what's happening and would appreciate advice on how to solve this.

If I rebooted the Kobo and reconnecting it to my PC the book then seems to show up on Calibre as well.

On one occasion, after a lot of faffing about, most but not all of my books just disappeared from my Kobo as well, but logging out and in sort of rebuilt the database and restored all my books or something somehow.