iOS 8.4 deleted ALL my 100s of PDFs from me iPad Air

Why has iOS 8.4 removed PDFs from iBooks on the iPad? I had hundreds of PDFs in categories in iBooks on my iPad Air and when I upgraded to iOS 8.4, the first sync erased all of them. Subsequent attempts to select them all again, in iTunes and to sync have also failed. The organization I had established took two years to set up and add the appropriate material to. Anyone from Apple want to come over here and fix this mess?