Not really a reply, but an addition to your problem... Having same thing, started a while back(after a Dell "push" update). Lost the whole library. Uninstalled and re-installed couple times, then worked for a while. Then yesterday, bam... All gone. I tried to add to library, but got the message that the book was already in the library.
I deleted the program again, and manually deleted all the folders and files under the "documents" folder where the digital editions info had previously been stored. Re-installed and still no library. Still could not add items once in the library for same reason as above. However, the files I had previously manually deleted were back. Clicking on the file directly in file explorer no longer worked either.
So, that brand new copy of Mississippi Blood by Greg Iles I just got... I added it, opened it once, closed it, and now it's gone. I still have the file, but cannot open it.
I also get the message that the book I am downloading is already in the library. I just have no idea where the library went.