Swift - array seems empty even after filling it with data

I am having a really weird problem at the moment and I have no clue why this happens.

First I retrieve some documents from my Cloud-FirestoreDB. This works perfectly fine.

func retrieveUserDataFromDB() -> Void {

    // local mutable "WishList" var
    var wList: [Wish] = [Wish]()

    let db = Firestore.firestore()
    let userID = Auth.auth().currentUser!.uid
    db.collection("users").document(userID).collection("wishlists").order(by: "listIDX").getDocuments() { ( querySnapshot, error) in
        if let error = error {
            print(error.localizedDescription)
        }else {
            // get all documents from "wishlists"-collection and save attributes
            for document in querySnapshot!.documents {
                let documentData = document.data()
                let listName = documentData["name"]
                let listImageIDX = documentData["imageIDX"]

                // if-case for Main Wishlist
                if listImageIDX as? Int == nil {
                    self.wishListImagesArray.append(UIImage(named: "iconRoundedImage")!)
                    self.wishListTitlesArray.append(listName as! String)
                    // set the drop down menu's options
                    self.dropDownButton.dropView.dropDownOptions.append(listName as! String)
                    self.dropDownButton.dropView.dropDownListImages.append(UIImage(named: "iconRoundedImage")!)
                }else {
                    self.wishListTitlesArray.append(listName as! String)
                    self.wishListImagesArray.append(self.images[listImageIDX as! Int])
                    self.dropDownButton.dropView.dropDownOptions.append(listName as! String)
                    self.dropDownButton.dropView.dropDownListImages.append(self.images[listImageIDX as! Int])
                }

                // create an empty wishlist
                wList = [Wish]()
                self.userWishListData.append(wList)

                // reload collectionView and tableView
                self.theCollectionView.reloadData()
                self.dropDownButton.dropView.tableView.reloadData() 

            }
        }
    }

    // un-hide the collection view
    self.theCollectionView.isHidden = false

    getWishes()

}

As you can see in the function above I also .append my wishListTitlesArray. However if I try to access the data inside of it nothing happens..

func getWishes (){
    let db = Firestore.firestore()
    let userID = Auth.auth().currentUser!.uid

    var counter = 0
    print("yikes")

    for list in self.wishListTitlesArray {
        print("yeet")
        db.collection("users").document(userID).collection("wishlists").document(list).collection("wünsche").getDocuments() { ( querySnapshot, error) in
            if let error = error {
                print(error.localizedDescription)
            }else{
                var wList = self.userWishListData[counter]
                for document in querySnapshot!.documents {
                    let documentData = document.data()
                    let wishName = documentData["name"]
                    wList.append(Wish(withWishName: wishName as! String, checked: false))
                    counter += 1
                    print("hi")
                    print(wishName as! String)
                }
            }
        }
    }
}

Right now it is printing the print("yikes") so it is not even going inside the for-loop.

I also tried printing all the elements in the end of func retrieveUserDataFromDB but that doesn't doing anything either. It is not crashing or showing any error.

Probably just a stupid mistake but if anyone has any idea why this happens I would be very grateful!