Code to reproduce a Mapbox Navigation bug where polylines disappear from the map when transitioning to night

ChildNavigationViewControllerBug.swift

import MapboxDirections
import MapboxCoreNavigation
import MapboxNavigation
 
class ViewController: UIViewController {
    
    var mbNavigationController: NavigationViewController!
    
    let addNavigationViewControllerAsChild = true
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        // Define two waypoints to travel between
        let origin = Waypoint(coordinate: CLLocationCoordinate2D(latitude: 38.9131752, longitude: -77.0324047), name: "Mapbox")
        let destination = Waypoint(coordinate: CLLocationCoordinate2D(latitude: 38.8977, longitude: -77.0365), name: "White House")
        
        // Set options
        let routeOptions = NavigationRouteOptions(waypoints: [origin, destination])
        
        // Request a route using MapboxDirections.swift
        Directions.shared.calculate(routeOptions) { (session, result) in
            switch result {
            case .failure(let error):
                print(error.localizedDescription)
            case .success(let response):
                guard let route = response.routes?.first else {
                    return
                }
                
                // Pass the first generated route to the the NavigationViewController
                let service = MapboxNavigationService(
                    route: route,
                    routeIndex: 0,
                    routeOptions: routeOptions,
                    directions: nil,
                    locationSource: nil,
                    eventsManagerType: nil,
                    simulating: .always,
                    routerType: nil)
                
                let navigationOptions = NavigationOptions(
                    styles: nil,
                    navigationService: service,
                    voiceController: nil,
                    topBanner: nil,
                    bottomBanner: nil
                )
                
                self.mbNavigationController = NavigationViewController(
                    for: route,
                    routeIndex: 0,
                    routeOptions: routeOptions,
                    navigationOptions: navigationOptions
                )
              
                self.mbNavigationController.automaticallyAdjustsStyleForTimeOfDay = true
                
                if self.addNavigationViewControllerAsChild {
                    // When adding as a child, day/night transitions can cause the route polyline to disappear from the map
                    // if the view that gets force refreshed is the superview of mbNavigationController.
                    
                    // Capture the delegate so that we can customize styleManager(_:viewForApplying:).
                    self.mbNavigationController.styleManager.delegate = self
                    
                    self.view.addSubview(self.mbNavigationController.view)
                    self.addChild(self.mbNavigationController)
                    self.mbNavigationController.didMove(toParent: self)
                    
                    // If styleManager(_:viewForApplying:) returns the mbNavigationController's view, which is its default
                    // implementation, then we must we must use autoresizing masks instead of autolayout constraints for
                    // framing the child. This is because the superview of mbNavigationController's view will have its
                    // subviews removed and then readded via StyleManager forceRefreshAppearance(). In the default case, that
                    // superview is self.view.
                    self.mbNavigationController.view.autoresizingMask = [.flexibleWidth, .flexibleHeight]
                    
                } else {
                    // When presenting modally, day/night transitions do not break the polyline. No need to capture the styleManager delegate.
                    
                    self.mbNavigationController.modalPresentationStyle = .fullScreen
                    self.present(self.mbNavigationController, animated: true, completion: nil)
                }
            }
        }
    }
}


/// This extension is only used when `addNavigationViewControllerAsChild` is true.
extension ViewController: StyleManagerDelegate {
    
    func styleManager(_ styleManager: StyleManager, viewForApplying currentStyle: Style?) -> UIView? {
        
        // StyleManager's forceRefreshAppearance() will use the superview of whatever view is returned in this delegate.
        // - if shouldReturnOneLevelHigher == true, this will end up using self.view.superview and the polyline won't disappear.
        // - if shouldReturnOneLevelHigher == false, this will end up using self.view and the polyline will disappear.
        
        let shouldReturnOneLevelHigher = false
        
        if shouldReturnOneLevelHigher {
            return self.view
        } else {
            // The default implementation will return mbNavigationController.view.
            return mbNavigationController.styleManager(styleManager, viewForApplying: currentStyle)
        }
    }
    
    func location(for styleManager: StyleManager) -> CLLocation? {
        mbNavigationController.location(for: styleManager)
    }
    
    func styleManager(_ styleManager: StyleManager, didApply style: Style) {
        mbNavigationController.styleManager(styleManager, didApply: style)
    }
    
    func styleManagerDidRefreshAppearance(_ styleManager: StyleManager) {
        mbNavigationController.styleManagerDidRefreshAppearance(styleManager)
    }
}