Loading UIImage in CollectionView Cell movement freezes - swift

Question

I have a UICollectionViewCell with 1 to 3 UIImageView that are managed by a stackView.
The Images all have around 8mb. I load them async from CoreData before calling collectionView.reload()
In this setup the collection view freezes when moving while loading new cells.
I tried it with smaller Images and then it did not freeze.
I now scale the Images down before loading them in to the UIImageView. But it leads to other weird behaviour like first showing the picture from the other cell and then adding the correct ones.
override func configureCellAtIndexPath(item: Journaling) {
super.configureCellAtIndexPath(item: item)
let imageOne = UIImageView()
let imageTwo = UIImageView()
let imageThree = UIImageView()
imageContainer = nil
imageOne.image = nil
imageTwo.image = nil
imageThree.image = nil
if item.image.count == 1 {
let group = DispatchGroup()
group.enter()
var downsizedImage = [UIImage]()
DispatchQueue.global().async {
downsizedImage.append(item.image[0].downsizeImage(.low)!)
group.leave()
}
group.notify(queue: .main) {
imageOne.image = downsizedImage[0]
imageTwo.image = nil
imageThree.image = nil
self.setUpStackView([imageOne])
}
}
if item.image.count == 2 {
let group = DispatchGroup()
group.enter()
var downsizedImage = [UIImage]()
DispatchQueue.global().async {
downsizedImage.append(item.image[0].downsizeImage(.low)!)
downsizedImage.append(item.image[1].downsizeImage(.low)!)
group.leave()
}
group.notify(queue: .main) {
imageOne.image = downsizedImage[0]
imageTwo.image = downsizedImage[1]
imageThree.image = nil
self.setUpStackView([imageOne,imageTwo])
}
}
if item.image.count > 2 {
let group = DispatchGroup()
group.enter()
var downsizedImage = [UIImage]()
DispatchQueue.global().async {
downsizedImage.append(item.image[0].downsizeImage(.low)!)
downsizedImage.append(item.image[1].downsizeImage(.low)!)
downsizedImage.append(item.image[2].downsizeImage(.low)!)
group.leave()
}
group.notify(queue: .main) {
imageOne.image = downsizedImage[0]
imageTwo.image = downsizedImage[1]
imageThree.image = downsizedImage[2]
self.setUpStackView([imageOne,imageTwo,imageThree])
}
}
imageOne.contentMode = .scaleAspectFill
imageOne.clipsToBounds = true
imageTwo.contentMode = .scaleAspectFill
imageTwo.clipsToBounds = true
imageThree.contentMode = .scaleAspectFill
imageThree.clipsToBounds = true
}
func setUpStackView(_ views: [UIView]) {
self.imageContainer = UIStackView(arrangedSubviews: views)
self.imageContainer.axis = .horizontal
self.imageContainer.distribution = .fillEqually
placeholder.sv(imageContainer)
imageContainer.addConstrainsToSuperView(distance: 0, superView: placeholder)
}