You still have not fixed your bug and I know you are simply not interested in fixing it.

Hi, Thanks for your help but as I know exactly how the file is structured (it becomes a read only data file) I managed to read it with no problem using similar functions from my Objective-C code. Regards, Paul

Apple did slightly fix their bug but not 100% fixed. It's now been 2 years and the ticket is still open. Doesn't matter anymore as the schools which were using my app have moved to ChromeBooks and we have an online site especially for them.

Found it, fixed it. recorderDefaults = [AVFormatIDKey: Int(kAudioFormatMPEG4AAC), AVEncoderAudioQualityKey: AVAudioQuality.min.rawValue] Don't use kAudioFormatMPEG4AAC.

What a surprise! Apple's bug still exits in 15.1. How do I claim, from Apple, lost revenue and the tarnish of our reputation because of Apple's inability and/or indifference to fix this bug?

More info... Apple's bug first appeared in iOS 14, iOS 8,9,10,11,12,13 had no problem. My data for the App was created on macOS 10.9 (or earlier, don't remember) and I've noticed reconstructing the data was no problem on subsequent flavours of macOS until Big Sur which now has the same bug as in iOS14 - it shows exactly the same problem when rendering a PDF. The PDF displays without problem in Safari, Adobe, Microsoft Edge, IE, and Firefox, Opera, Brave, Chrome on Linux and Windows. Obviously it's something Apple did.