All content inside iBooks disappeared Title is self-explenatory. I really didn't do anything special, all epubs, PDFs etc are gone. I restarted the computer, same result. I have only used it from my MacBook, no iPhone, iPad or anything else.

I checked time machine at username&gt;library&gt;contents&gt;com.apple.BKAgentService&gt;data&gt;documents&gt;ibooks&gt;books and weirdly I could only find books starting from many months ago and not sooner. For at least the last 3-4 backups this folder was empty, which is insane as I use iBooks every day and that definitely wasn't the case until now. 

I restored these books, copy and pasted them at the present time username&gt;library&gt;contents&gt;com.apple.BKAgentService&gt;data&gt;documents&gt;ibooks&gt;books folder but to no avail.

This is so weird as we're talking about hundreds of books!

Is there a standard dumb thing I may have unknowingly done for this to occur? What else can I try to resolve this?
My first instinct would be to try logging out of the iBooks Store and then logging back in. You can do this as follows:


Launch iBooks
Go to Store > Sign Out
Wait about 30 seconds and then go to Store > Sign In...
Enter your Apple ID and Password
Click on Sign In
Click on Get Started
iBooks should now populate with all your books, PDFs etc.