iOS 13 - frameloss while using kAudioFormatLinearPCM

my App is recording audio with

kAudioFormatLinearPCM

set up in der

AudioStreamBasicDescription

. It all works fine on iOS12 (checked by downloading the container). After updating to iOS13 the audio file is saved correctly but when reopening the file, a wrong frame count is returned.The audio is unusable.

We are using a mix of swift and objective c code.

My

AudioStreamBasicDescription

:

self.audioFormat = AudioStreamBasicDescription( 
mSampleRate: Double(self.hardwareSampleRate), 
mFormatID: kAudioFormatLinearPCM, 
mFormatFlags: ( kAudioFormatFlagIsSignedInteger | kAudioFormatFlagIsPacked ), 
mBytesPerPacket:    4, 
mFramesPerPacket:   1, 
mBytesPerFrame:     4, 
mChannelsPerFrame:  1, 
mBitsPerChannel:    32, 
mReserved:          0 ); 

self.audioPlot = XOAudioPlotGL(); 
self.audioPlot.initialize(withSourceAudioFormat: self.audioFormat);

hardwareSampleReate = 44100

And reopening the file:

CheckError(ExtAudioFileOpenURL(readURL, &mAudioFileRef), "Error: Open File"); 
CheckError(ExtAudioFileSetProperty(mAudioFileRef,kExtAudioFileProperty_ClientDataFormat, sizeof(audioFormat), &audioFormat), "Set Client Data Format"); 
CFRelease(readURL);  

UInt32 propSize = sizeof(SInt64); 
UInt32 numberOfFrames = 0; 
CheckError(ExtAudioFileGetProperty(mAudioFileRef, kExtAudioFileProperty_FileLengthFrames, &propSize, &numberOfFrames), "Get Number of Frames");

Here a lower framenumber is returned.

I don't see a reason why this all would work on iOS12 but not on iOS13.

Please let me know if I missed something or more details are needed.

Any help is appreciated.