iBooks are not synchronized via iCloud between my Apple devices
Open Settings app on both devices and verify both have an iCloud backup (or connect to iTunes and back up both)
Sign out of iTunes &amp; App Store and then reboot both devices
Sign back in to the iTunes &amp; App store on one device
Open iBooks and see what it shows for your purchases / books.
Tap to download one of each (a purchased book and a synced book)
Then review the iBooks settings in the settings app for this device


Repeat the sign in steps for the second iOS device. Pay attention to the "Sync Collections" setting for iBooks.