NSCache Doesn't work with all images when loading for the first time

I'm woking on a project in swift 3.0 where I cache the response from the server by using NSCache as to populate them in a UITableView. However for some reason I'm only seeing few images loading when the app loads for the first time, but if If i scroll and come back I see everything (end of retrieving the response from the server I reload my tableview too, but seems that not the case). I'm not sure what I''m exactly missing here, the code as bellow as to show how I cache the images.

let imageCache = NSCache<AnyObject, AnyObject>()
var imageURLString : String?

extension UIImageView {


    public func imageFromServerURL(urlString: String) {
        imageURLString = urlString

        if let url = URL(string: urlString) {

            image = nil


            if let imageFromCache = imageCache.object(forKey: urlString as AnyObject) as? UIImage {

                self.image = imageFromCache

                return
            }

            URLSession.shared.dataTask(with: url, completionHandler: { (data, response, error) in

                if error != nil{
                    print(error as Any)


                    return
                }

                DispatchQueue.main.async(execute: {

                    if let imgaeToCache = UIImage(data: data!){

                        if imageURLString == urlString {
                            self.image = imgaeToCache
                        }

                        imageCache.setObject(imgaeToCache, forKey: urlString as AnyObject)// calls when scrolling
                    }
                })
            }) .resume()
        }
    }
}