//This is what you're doing

upload(image: image!, to: "Users/\(Auth.auth().currentUser!.uid)/photoUrls/0", completion: { urlString, error in
                Database.database().reference().child("Users/\(Auth.auth().currentUser!.uid)/photoUrls/0").setValue(urlString)
            },
                Database.database().reference().child("Users/\(Auth.auth().currentUser!.uid)/photoUrls/0").observeSingleEvent(of: .value) { (snapshot) in
                    let urlString = snapshot.value as! String
                    let task = URLSession.shared.dataTask(with: URL(string: urlString)!) {(data, response, error) in

                        if let image: UIImage = UIImage(data: data!) {
                            DispatchQueue.main.async {
                                //update the image
                                self.ProfileImage.image = image
                            }
                        }
                    }
                    task.resume()
                }
                   )}



//This is what you should do:
//Upload the image
upload(image: image!, to: "Users/\(Auth.auth().currentUser!.uid)/photoUrls/0", completion: {
    urlString, error in
    Database.database().reference().child("Users/\(Auth.auth().currentUser!.uid)/photoUrls/0").setValue(urlString)
})

//Grab the image (it won't be available right away as "upload" is an asynchronous function)
Database.database().reference().child("Users/\(Auth.auth().currentUser!.uid)/photoUrls/0").observeSingleEvent(of: .value) {
    (snapshot) in
    let urlString = snapshot.value as! String
    let task = URLSession.shared.dataTask(with: URL(string: urlString)!) {
        (data, response, error) in
        if let image: UIImage = UIImage(data: data!) {
            DispatchQueue.main.async {
                //update the image
                self.ProfileImage.image = image
            }
        }
    }

    task.resume()
}