Not sure if I should be using a real time database - ios

Question

Currently having trouble displaying all highscores from my firebase realtime database. At the moment I'm only displaying "live" scores.
I am currently making a score board, where the top 50 scores and their usernames are displayed in a table. This works fine. However I am unsure as to whether I should be using a Real-Time database.
You see, when I do a fresh build on my physical device and create a new user, the user is saved into the Firebase database and when I achieve a new score and push to display highscore users, my new user is rightfully there with their score.
If I log out (but am still within the app) and register with a new user, and then play again (with the new user), and then I click to see the highscores leaderboard again I can now see both of the users I have created, with their scores. GREAT!
I can check the Authentication part of firebase, and sure enough, my users are in there with their email and passwords etc. And I can check their highscores on the Real-Time database. All is well.
However, when I delete the app from my device or even push it into the background, and then do a fresh build, or re-open the app. The authentication details (password, username, email) are still there, but when I open the Real-Time database, there is no data there.
Consequently, when I click to see the highscores leaderboard, there is nothing to show. Is this because I should not be using a realtime database, is it only displaying “live/recent data” and doesn't actually store the data I want permanently. Should I be using SQL or something else?
This is the code to add my highscore to my database......
func addingScoreToFB() {
let currentUser = Auth.auth().currentUser
let highScore = UserDefaults.standard.integer(forKey: highScoreIdentifier)
let recentScore = UserDefaults.standard.integer(forKey: recentScoreIdentifier)
if let userID = currentUser?.uid {
let userDB = Database.database().reference().child("Users").child(userID)
if recentScore > highScore {
let highSDictionary = ["highScore":self.recentScores.last!]
userDB.updateChildValues(highSDictionary as Any as! [AnyHashable : Any], withCompletionBlock: { (err, ref) in // Adding Score
if let err = err {
print(err)
}
})
}
}
}
This is my code to display the scores.....
func retrieveUserData() {
let postsRef = self.ref.child("Users")
let query = postsRef.queryOrdered(byChild: "highScore").queryLimited(toLast: 50)
query.observeSingleEvent(of: .value, with: { snapshot in
for child in snapshot.children {
let snap = child as! DataSnapshot
let dict = snap.value as! [String: Any]
let name = dict["username"] as! String
let score = dict["highScore"] as! Int
let aScore = ScoreClass(withName: name, andScore: score)
self.scoresArray.insert(aScore, at: 0)
}
self.topScoresTableView.reloadData()
})
}
In summary I would like to be able to see the top 50 scores of every user in the database of all time, but I am currently only seeing the recent ones on a new build.