App freezes my whole phone, just by clicking on launch icon - ios

Question

I am a new developer, and I am currently making my first app.
Sometimes when I try to open the app, the icon dims, but nothing happens, and the whole phone briefly becomes unresponsive. My guess is this is happening in app delegate. I'm not sure what is happening, but I think I should be using grand central dispatch.
this is currently my code in app delegate,
import UIKit
import Firebase
import FirebaseMessaging
#UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {
var window: UIWindow?
func application(application: UIApplication, didFinishLaunchingWithOptions launchOptions: [NSObject: AnyObject]?) -> Bool {
//Facebook SharedInstance FBSDKApplicationDelegate.sharedInstance().application(application, didFinishLaunchingWithOptions: launchOptions)
//Firebase Database
FIRApp.configure()
FIRDatabase.database().persistenceEnabled = true
//Onesignal PushNotifications
_ = OneSignal(launchOptions: launchOptions, appId: "3b2b4845-0b6a-4e92-892f-254c2cf51da8", handleNotification: nil)
_ = OneSignal(launchOptions: launchOptions, appId: "3b2b4845-0b6a-4e92-892f-254c2cf51da8", handleNotification: { (message, additionalData, isActive) in
NSLog("OneSignal Notification opened:\nMessage: %#", message)
if additionalData != nil {
NSLog("additionalData: %#", additionalData)
// Check for and read any custom values you added to the notification
// This done with the "Additonal Data" section the dashbaord.
// OR setting the 'data' field on our REST API.
if let customKey = additionalData["customKey"] as! String? {
NSLog("customKey: %#", customKey)
}
}
}, autoRegister: true)
print("didFinishLaunchingWithOptions launchOptions")
return true
}
func application(application: UIApplication, openURL url: NSURL, sourceApplication: String?, annotation: AnyObject) -> Bool {
print("application")
return FBSDKApplicationDelegate.sharedInstance().application(application, openURL: url, sourceApplication: sourceApplication, annotation: annotation)
}
Is it possible, that this has nothing to do with app delegate?
if it is in app delegate how can use GCD to make this work

Answer 1

remove
import FirebaseMessaging
and
FIRDatabase.database().persistenceEnabled = true
from the AppDeleget and try running it