Flutter iOS - EXC_BAD_ACCESS crash on cold start after app was killed, affects ~1-2% of users

Question: How to prevent Flutter app crash on iOS 18 during cold start when iOS traverses view hierarchy before Flutter engine is fully initialized?

Help needed: Looking for a way to either delay iOS view hierarchy traversal or ensure Flutter is fully initialized before iOS lifecycle callbacks fire.

Problem Summary

Our Flutter app crashes on cold start for approximately 1-2% of iOS users. The crash occurs specifically on iOS and only under these exact conditions:

When crash happens:

1. User opens app and uses it normally ✅
2. User minimizes app (goes to background) ✅
3. User returns to app from background ✅ (works fine)
4. User kills app from app switcher (swipe up to close)
5. User taps app icon to launch again → CRASH ❌

Key observations:

• Crash is intermittent - app may open on 2nd, 3rd, or 5th attempt
• 100% reproducible on affected devices by repeating kill→launch cycle
• ~98% of users have no issues

Environment

• Flutter: 3.38.3

Crash Logs (from Sentry)

Crash Type 1: Stack Overflow (most common)

OS Version: iOS 18.7.2 (22H124) Exception Type: EXC_BAD_ACCESS (SIGBUS) Exception Codes: BUS_NOOP at 0x000000016ad5be90

Application Specific Information: compare:options:range:locale: > Stack overflow in (null)

Thread 0 Crashed: 0 CoreFoundation CFStringGetLength 1 CoreFoundation CFStringCompareWithOptionsAndLocale 2 CoreFoundation <redacted> 3 libsystem_c bsearch 4 CoreFoundation <redacted> 5 UIKitCore <redacted> ... 15-99: UIKitCore 0x30e177148 [inlined] <redacted> // 85+ recursive calls

Crash Type 2: Use-After-Free

Exception Type: EXC_BAD_ACCESS (SIGSEGV) Exception Codes: SEGV_NOOP at 0x0500007f14000000 KERN_INVALID_ADDRESS at 0x500007f14000000

Thread 0 Crashed: 0 libobjc.A.dylib objc_retainAutoreleaseReturnValue 1 UIKitCore <redacted> ... 6 libobjc.A.dylib objcrootDealloc 7 QuartzCore <redacted> // CALayer operations

What We Tried (nothing solved cold start crash)

Current AppDelegate.swift

import UIKit import Flutter

@main

@objc

class AppDelegate: FlutterAppDelegate {

private var snapshotView: UIView?
private var isAppActive = false

override func application(
    _ application: UIApplication,
    didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?
) -> Bool {
    GeneratedPluginRegistrant.register(with: self)
    window?.overrideUserInterfaceStyle = .light
    isAppActive = true
    return super.application(application, didFinishLaunchingWithOptions: launchOptions)
}

override func application(_ application: UIApplication, shouldSaveSecureApplicationState coder: NSCoder) -> Bool {
    return false
}

override func application(_ application: UIApplication, shouldRestoreSecureApplicationState coder: NSCoder) -> Bool {
    return false
}

override func applicationWillResignActive(_ application: UIApplication) {
    guard isAppActive,
          let window = self.window,
          let rootVC = window.rootViewController,
          rootVC.isViewLoaded,
          snapshotView == nil
    else { return }

    let snapshot = UIView(frame: window.bounds)
    snapshot.backgroundColor = .white
    snapshot.tag = 999
    window.addSubview(snapshot)
    snapshotView = snapshot
}

override func applicationDidBecomeActive(_ application: UIApplication) {
    guard snapshotView != nil else {
        isAppActive = true
        return
    }

    snapshotView?.removeFromSuperview()
    snapshotView = nil
}

}