Memory usage issue with PHAssetResource.assetResources() call

Question

I am testing the following codes

// firstly list all the assets in the Photos.
let fetchOptions = PHFetchOptions()
fetchOptions.sortDescriptors = [NSSortDescriptor(key: "creationDate", ascending: false)]
fetchOptions.predicate = NSPredicate(format: "mediaType = %d || mediaType = %d", PHAssetMediaType.image.rawValue, PHAssetMediaType.video.rawValue)

let assets = PHAsset.fetchAssets(with: fetchOptions)
let totalAssetCount = assets.count

for index in 0...(totalAssetCount-1) {
    let asset = assets.object(at: index)

    autoreleasepool{
        var resource = PHAssetResource.assetResources(for: asset)
    }
}

And I can see that the above codes have severe memory leak issue with the following operation (memory usage continues to grow until all the images are looped, and it never goes down even when the loop finishes).

var resource = PHAssetResource.assetResources(for: asset)

Even with the autoreleasepool, the memory never gets released. Also the symptom is gone when I comment out the PHAssetResource.assetResources(). So is there any resource usage issue with the PHAssetResource.assetResources() function in swift? If so, how can I resolve and workaround these problems?

I noticed previous posts here PHAssetResource.assetResources(for: asset).first.OriginalFilename gives nil after 300 assets but apparently adding the autoreleasepool call does not help me at all.