AVAssetExportSession fails to export videos downloaded from iCloud

I'm trying to create a scaled down version of a video selected from the users photo album. The max dimensions of the output will be 720p. Therefore, when retrieving the video, I'm using the .mediumQualityFormat as the deliveryMode.

This causes iOS to retrieve a 720p video from iCloud if the original video or its medium quality version don't exist in the users device.

Code Block swift
let videoRequestOptions = PHVideoRequestOptions()
videoRequestOptions.deliveryMode = .mediumQualityFormat
videoRequestOptions.isNetworkAccessAllowed = true
PHImageManager.default().requestAVAsset(forVideo: asset, options: videoRequestOptions) { (asset, audioMix, info) in
    // Proceess the asset
}

The problem is, when I use AVAssetExportSession to create a scaled down version of the asset, if the asset is a medium variant and not the original version, the export process fails immediately with the following error:

Code Block 
Error Domain=AVFoundationErrorDomain Code=-11800 "The operation could not be completed" UserInfo={NSLocalizedFailureReason=An unknown error occurred (-17507), NSLocalizedDescription=İşlem tamamlanamadı, NSUnderlyingError=0x283bbcf60 {Error Domain=NSOSStatusErrorDomain Code=-17507 "(null)"}}

I couldn't find anything about the meaning of this error anywhere.

When I set the deliveryMode property to .auto or .highQualityFormat, everything is working properly.

When I checked the asset url's, I noticed that if the video has been retrieved from iCloud, its filename has a ".medium" postfix like in this example:

Code Block 
file:///var/mobile/Media/PhotoData/Metadata/PhotoData/CPLAssets/group338/191B2348-5E19-4A8E-B15C-A843F9F7B5A3.medium.MP4

The weird thing is, if I use FileManager to copy the video in this url to another directory, create a new AVAsset from that file, and use that asset when creating the AVExportSession instance, the problem goes away.

I'd really appreciate if someone could provide some insight about what the problem could be.

This is how I use AVAssetExportSession to create a scaled down version of the original video.

Code Block swift
let originalVideoURL = "The url of the asset retrieved from requestAVAsset"
let outputVideoPath = NSTemporaryDirectory() + "encodedVideo.mp4"
let outputVideoURL = URL(fileURLWithPath: outputVideoPath)
guard
        let exportSession = AVAssetExportSession(asset: asset, presetName: AVAssetExportPresetHighestQuality),
        let videoTrack = asset.tracks(withMediaType: .video).first else {
      handleError()
    return
}
let videoComposition = AVMutableVideoComposition()
videoComposition.renderSize = scaledSize 
videoComposition.frameDuration = CMTimeMake(value: 1, timescale: 30)
let layerInstruction = AVMutableVideoCompositionLayerInstruction(assetTrack: videoTrack)
let transform = videoTrack.preferredTransform
layerInstruction.setTransform(transform, at: .zero)
let instruction = AVMutableVideoCompositionInstruction()
instruction.timeRange = CMTimeRangeMake(start: .zero, duration: asset.duration)
instruction.layerInstructions = [layerInstruction]
videoComposition.instructions = [instruction]
exportSession.videoComposition = videoComposition
exportSession.outputURL = outputVideoURL
exportSession.outputFileType = .mp4
exportSession.shouldOptimizeForNetworkUse = true
exportSession.exportAsynchronously(completionHandler: {[weak self] in
    guard let self = self else { return }
    if let url = exportSession.outputURL, exportSession.status == .completed {
        // Works for local videos
    } else {
        // Fails with error code 17507 when loading videos with delivery size "Medium"
    }
})