Since updating to iOS 12 iBooks app freezes on iPad Pro

Updated to iOS 12 several days ago. Since the update my iBooks app library is no longer working properly and freezes each time I try to open an item in it. Sometimes this also freezes the whole iPad. Have shut down and restarted iPad several times and the problem persists. I can open items in other parts of iBooks (eg ‘Reading Now’), just not anything in the library. Once I tap on Library the app totally freezes and I need to close it. Previously I was able to share/save a PDF from an email to iBooks and it would open immediately in iBooks. Now when I try this iBooks opens and tries to open the PDF but then my whole iPad just totally freezes and I need to shut down and restart it. The same problem is happening on my iPhone. My icloud backup is up to date. Thanks for any suggestions!