Downloading multiple HLS audio files simultaneously fails - ios

Question

I have been trying to multiple HLS audio files together in iOS. The files are encrypted with a key. I need to fetch the key and store it locally for offline use. When I download a small number (2 or 3 files) of files simultaneously it works fine, but if I start downloading 10-15 files simultaneously most of them fails with the error message-
Error Domain=AVFoundationErrorDomain Code=-11800 "The operation could
not be completed" UserInfo={NSLocalizedFailureReason=An unknown error
occurred (-17377), NSLocalizedDescription=The operation could not be
completed}
I am getting error message from NSURLErrorDomain as well but they are rare.
The link of the approach which I am using to fetch the key for offline use is below -
Playing Offline HLS with AES-128 encryption iOS
Any help would be appreciated.
class AudioDownloader {
var productKey: String
var downloadUrl: URL
var downloadSession: AVAssetDownloadURLSession?
var fakeDownloadUrl: URL?
var downloadTask: AVAssetDownloadTask?
func downloadAudio() {
if downloadSession == nil {
let configuration = URLSessionConfiguration.background(withIdentifier: self.productKey)
downloadSession = AVAssetDownloadURLSession(configuration: configuration, assetDownloadDelegate: self, delegateQueue: OperationQueue.main)
configuration.shouldUseExtendedBackgroundIdleMode = true
configuration.httpShouldSetCookies = true
configuration.httpShouldUsePipelining = false
configuration.allowsCellularAccess = true
configuration.isDiscretionary = true
}
self.fakeDownloadUrl = self.convertToScheme(url: self.downloadUrl, scheme: "fakehttp")
let asset = AVURLAsset(url: self.fakeDownloadUrl!)
let loader = asset.resourceLoader
loader.setDelegate(self, queue: DispatchQueue(label: "dispatch2"))
self.downloadTask = downloadSession?.makeAssetDownloadTask(asset: asset, assetTitle: "assetTitle \(self.productKey)", assetArtworkData: nil, options: nil)!
self.downloadTask?.taskDescription = self.productKey
self.downloadTask?.resume()
}
}