Error Domain=NSOSStatusErrorDomain Code=-54 "(null)" in AVAudioPlayer

I've been struggling with this error and I can't understand where it is coming from. I'm picking a file from the Files app within my App. It returns a correct URL (file:///private/var/mobile/Library/Mobile%20Documents/com~apple~CloudDocs/sound.mp3).

However, when trying to play it with AVAudioPlayer, it gives me the Error Domain=NSOSStatusErrorDomain Code=-54 "(null)". I suspect this is related to permissions or something, but I cannot find how to overcome it. When adding the file to the assets in the project, it plays fine.

Any clue?

The code I'm using is the following:

func documentPicker(_ controller: UIDocumentPickerViewController, didPickDocumentsAt urls: [URL]) {
    guard controller.documentPickerMode == .open, let url = urls.first, url.startAccessingSecurityScopedResource() else {
        return
    }
    defer {
        url.stopAccessingSecurityScopedResource()
    }
    do {
        print("Playing \(url)")
        try audioPlayer = AVAudioPlayer(contentsOf: url)
        print("preparing...")
        audioPlayer?.prepareToPlay()
        print("playing...")
        audioPlayer?.play()
    } catch {
        print(error)
    }
    controller.dismiss(animated: true, completion: nil)
}

Moreover, I have added the iCloud Documents entitlements...