ios11 MKAnnotation not showing both annotations

Question

When I add the annotations to the map they sometimes show and sometimes not depending on how close they are to each other. If they are in the same house lets say one won't show. How do I make both of them show? Do I need to make a custom annotation class? I heard ios11 has a clumping feature, do I need to use that? Here is the code(abridged):

import UIKit
import MapKit
import Firebase

class GameViewController: UIViewController {


@IBOutlet weak var mapView: MKMapView!

fileprivate var locations = [CLLocation]()
fileprivate var userLocations = [(loc: CLLocation, name: String, team: String)]()
fileprivate var userAnnotations = [MKAnnotation]()
fileprivate var hasBeenUP = false

var ref: FIRDatabaseReference!
let uid = FIRAuth.auth()!.currentUser!.uid

var timer = Timer()
var timeLeft = 0.0
var firstTimer = Timer()

var name = ""
var team = ""

override func viewDidLoad() {
    super.viewDidLoad()
    let center = CLLocationCoordinate2D(latitude: 47.786769, longitude: -20.413634)
    let region = MKCoordinateRegion(center: center, span: MKCoordinateSpan(latitudeDelta: 0.01, longitudeDelta: 0.01))
    self.mapView.setRegion(region, animated: true)
    mapView.mapType = .hybrid
    locationManager.startUpdatingLocation()

    ref = FIRDatabase.database().reference()

    setupULSending()
    getMetaInfo()

    ref.child("realtimeLocations").observe(FIRDataEventType.value, with: { (snapshot) in
        self.userLocations = []
        for rest in snapshot.children.allObjects as! [FIRDataSnapshot] {
            guard let snapshotValue = snapshot.value as? NSDictionary, let snapVal = snapshotValue[rest.key] as? NSDictionary else {
                break
            }
            let name = snapVal["name"] as! String
            let team = snapVal["team"] as? String ?? ""
            if let lat = snapVal["lat"] as? Double,
                let long = snapVal["long"] as? Double {
                let location = CLLocation(latitude: lat, longitude: long)
                self.userLocations.append((loc: location, name: name, team: team))
            }else {

            }
        }
        DispatchQueue.main.async {
            self.updateUserLocation()
        }
    })
}

private lazy var locationManager: CLLocationManager = {
    let manager = CLLocationManager()
    manager.allowsBackgroundLocationUpdates = true
    manager.desiredAccuracy = kCLLocationAccuracyBest
    manager.delegate = self
    manager.requestAlwaysAuthorization()
    return manager
}()

func updateUserLocation() {

    for an in self.mapView.annotations {
        mapView.removeAnnotation(an)
    }
    for loc in userLocations {
        let annotation = MKPointAnnotation()
        annotation.coordinate = loc.loc.coordinate
        annotation.title = loc.name
        annotation.subtitle = "local"
        mapView.addAnnotation(annotation)

    }
}

}

// MARK: - CLLocationManagerDelegate
extension GameViewController: CLLocationManagerDelegate {
  func locationManager(_ manager: CLLocationManager, didUpdateLocations 
  locations: [CLLocation]) {
    let location = locations.last as! CLLocation
    self.locations.append(location)
}
}

Answer 1

On the MKAnnotationView, you have to set the MKFeatureDisplayPriority to 'required'. You can modify the annotation views by implementing MKMapViewDelegate and mapView(MKMapView, viewFor: MKAnnotation). Something like this:

func mapView(_ mapView: MKMapView, viewFor annotation: MKAnnotation) -> MKAnnotationView? {
        if annotation is MKUserLocation { return nil }
        var view = mapView.dequeueReusableAnnotationView(withIdentifier: "yourIdentifier")
        if view == nil {
            view = MKMarkerAnnotationView(annotation: nil, reuseIdentifier: "yourIdentifier")
        }
        view?.displayPriority = .required
        return view
}

More options for this are explained in the WWDC 2017 video 237 "What's New in MapKit"