Firebase Anonymous Auth, Nil User - ios

Question

I'm using Firebase database and offer anonymous login. The first anonymous login made on a single device works as expected. If I sign out and attempt any more anonymous logins, it succeeds, the completion block has no error and returns a user.
However, once it's all done and we're out of the completion block, Auth.auth().currentUser() is nil.
If I run a simple Timer checking Auth.auth().currentUser() every second, throughout the entire login process it is always nil and never changes.
Quick breakdown of code:
Login anonymously.
Check if id exists in db.
Update profile displayName with id for easy referral later.
Fetch client in db.
All go wrong!
Tap a button to sign in.
#IBAction func clientLoginBtnTap(_ sender : UIButton) {
self.clientActivityIndicator?.showActivityIndicator()
Auth.auth().signInAnonymously { (user, error) in
if error == nil {
//check id matches available client
self.checkClient(id: (self.clientIdField?.text)!, completion: { (isValid) in
if isValid == true {
//now signed in, update client id
let profileChangeRequest = user?.createProfileChangeRequest()
profileChangeRequest?.displayName = self.clientIdField?.text
profileChangeRequest?.commitChanges(completion: { (error) in
if error == nil {
//done
UserDefaults.standard.set(true, forKey: kIS_USER_CLIENT_NOT_TRAINER)
self.dismiss(animated: true, completion: {
//self.delegate?.didLoginAsClient()
})
}
else {
self.logout()
self.clientIdField?.shake()
self.clientActivityIndicator?.hideActivityIndicator()
}
})
}
else {
self.logout()
self.clientIdField?.shake()
self.clientActivityIndicator?.hideActivityIndicator()
}
})
}
else {
}
}
}
func checkClient(id : String, completion: #escaping (_ isValid : Bool) -> Void) {
let ref = Database.database().reference().child("v2").child("clients").child(id)
ref.observeSingleEvent(of: .value, with: { (snapshot) in
if snapshot.exists() { completion(true) }
else { completion(false) }
}) { (error) in
completion(false)
}
}
func logout() {
do {
try Auth.auth().signOut()
}
catch let error as NSError {
print (error.localizedDescription)
}
}
Login is successful.
Then this runs after login and the user exists but Auth.auth().currentUser() is nil. When a client login happens, I try to get the client data but permission is denied because we have no user.
handle = Auth.auth().addStateDidChangeListener { (auth, user) in
self.currentUser = user
if user == nil {
self.updateForNoUser()
}
else {
self.updateForUser()
}
}
func updateForUser() {
//Trainer Logged in
if UserDefaults.standard.bool(forKey: kIS_USER_CLIENT_NOT_TRAINER) == false {
self.performSegue(withIdentifier: "master", sender: self)
}
//Client Logged in
else {
if let id = Auth.auth().currentUser?.displayName {
let ref = Database.database().reference().child("v2").child("clients").child(id)
ref.observeSingleEvent(of: .value, with: { (snapshot) in
if snapshot.exists() {
self.client = Client(snapshot: snapshot)
self.performSegue(withIdentifier: "masterClient", sender: self)
}
}) { (error) in }
}
else {
do {
try Auth.auth().signOut()
}
catch let error as NSError {
print (error.localizedDescription)
}
}
}
}