Some of the PDF books I added to iBooks are disappearing from my iPad. They also sometimes disappear from iBooks on my Mac. Yet, when I go to add the book to iBooks again, iBooks says I already have the book! For example, I have four Take Control books. Two appear in my library in iBooks on both iPad and Mac. One only appears on Mac. One appears in neither anymore!
I am using iCloud sync. I have turned everything off and back on. Rebooted everything. But this problem persists.
iMac with Retina 5K display, OS X El Capitan (10.11.2)
