After the update to 2.4.0 I had an issue with kepub.epub files, in that they had disappeared from the shelves, although I could see them in the book list with the option "buy now".
DomesticExtremis had the same problem, and it was suggested to re-load the book.
Problem is, I had a lot of annotations I did not want to lose, and whereas by clicking on the "buy now" icon produced a server error, I noticed that if clicking the book cover the book would open as normal, and would remember where you left off next time you opened it. Only, it would not show on the carousel, the cover would not show when sleeping, and the ominous "buy now" won't go away. Also, I wasn't very wise in making the point
in a thread dealing with something else entirely.
It turns out that the problem is in the sqlite database, and it can be fixed! I did try to open and explore the "content" tab of the database, but was pathetic enough with the search that I could not even find the right entries. Anyhow tshering fixed it for me - the problem was with the content.UserID, and I just reloaded the "tsheringfied" database. So thanks tshering
I thought I'd open this in case other people are experiencing the problem (or should the problem arise again with future firmware updates). I am not sure I understood exactly what he did, so I'll leave it to him to explain the details.