CGImageSourceCreateThumbnailAtIndex returns image with black background instead of transparent

I have several CGImages with transparent background and save it to one HEIC image with Image I/O

Code Block swift
func heic(from images: [CGImage]) -> Data? {
    guard
        let mutableData = CFDataCreateMutable(kCFAllocatorDefault, 0),
        let destination = CGImageDestinationCreateWithData(mutableData, "public.heic" as CFString, images.count, nil)
    else { return nil }
    for image in images {
        CGImageDestinationAddImage(
            destination,
            image,
            [
                kCGImageDestinationEmbedThumbnail: true,
                kCGImageDestinationLossyCompressionQuality: 1
            ] as CFDictionary
        )
    }
    guard CGImageDestinationFinalize(destination) else { return nil }
    return mutableData as Data
}

Then get thumbnail from HEIC data with CGImageSourceCreateThumbnailAtIndex

Code Block swift
func thumbnail(from data: Data, size: CGSize) -> CGImage? {
    guard let source = CGImageSourceCreateWithData(data as CFData, nil) else { return nil }
    guard let context = CGContext(
        data: nil,
        width: Int(size.width),
        height: Int(size.height),
        bitsPerComponent: 8,
        bytesPerRow: 0,
        space: CGColorSpaceCreateDeviceRGB(),
        bitmapInfo: CGImageAlphaInfo.premultipliedFirst.rawValue
    ) else { return nil }
    for index in 0 ..< CGImageSourceGetCount(source) {
        guard let image = CGImageSourceCreateThumbnailAtIndex(
            source,
            index,
            [
                kCGImageSourceCreateThumbnailFromImageIfAbsent: true,
                kCGImageSourceThumbnailMaxPixelSize: Int(max(size.width, size.height))
            ] as CFDictionary
        ) else { continue }
        context.draw(image, in: CGRect(origin: .zero, size: size))
    }
    return context.makeImage()
}

The problem is that resulting image has black background instead of transparent. I see this only on device (iPad Pro, iPadOS 14.2) not on simulator.

Also if I remove kCGImageDestinationEmbedThumbnail: true from destination properties, so that thumbnail not saved in Data, I receive correct thumbnail with transparent background from CGImageSourceCreateThumbnailAtIndex function.

What am I doing wrong? I want to have thumbnails in HEIC image and not create them in runtime on request.