Simple way to reproduce iOS bug - connecting Bluetooth Headphones while app is backgrounded.

AppDelegate.swift

//
//  AppDelegate.swift
//  ios-bluetooth-bug
//
//  Created by Nevo Segal on 08/10/2019.
//

import UIKit
import AVFoundation

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {

    let audioEngine = AVAudioEngine()

    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {

        do {
            try AVAudioSession.sharedInstance().setCategory(.playAndRecord,
                                            mode: .default,
                                             options: [.allowBluetoothA2DP,
                                                       .mixWithOthers,
                                                       .defaultToSpeaker,
                                                       .allowAirPlay])

            try AVAudioSession.sharedInstance().setActive(true)
        } catch {
            print(error.localizedDescription)
        }

        setup()
        start()
        NotificationCenter.default.addObserver(self, selector: #selector(handleConfigurationChange), name: .AVAudioEngineConfigurationChange, object: nil)
        return true
    }

    @objc func handleConfigurationChange() {
        //attempt to call start()
        //or to audioEngine.reset(), setup() and start()
        //or any other combination that involves starting the audioEngine
        //results in an error 561145187.
        //Not calling start() doesn't return this error, but also doesn't restart
        //the recording.
        print("received configration change notification")
        audioEngine.reset()
        audioEngine.inputNode.removeTap(onBus: 0)
        setup()
        start()
    }

    public func setup() {

        //Setup nodes
        let inputNode = audioEngine.inputNode
        let inputFormat = inputNode.inputFormat(forBus: 0)

        inputNode.installTap(onBus: 0, bufferSize: 4096, format: inputFormat) { (buffer, _) -> Void in
            //Do audio conversion and use buffers
        }
    }

    public func start() {
        guard !audioEngine.isRunning else {
            print("Audio Engine is already running")
            return
        }

        do {
            audioEngine.prepare()
            try audioEngine.start()
        } catch {
            print("Unable to start audio engine \(error.localizedDescription)")
        }
    }
}