iOS 9.3.1 has corrupted iBooks
I installed iOS 9.3.1 over 9.3.0 on my iPad 3/4 (128Gb WiFi-Cellular).
iBooks 4.7 was fine prior to the update, with various sub folders containing books by author and PDF categories. After the upgrade, all the sub folders are gone. I searched for an author, selected all the books in the search results and tried to move them to a new folder. The folder created, however none of the books moved are visible in that new folder. When iBooks is closed and reopened it just sits with the busy icon revolving in the top right hand corner.
iPad 2 Wi-Fi + 3G, iOS 9.3.1, null