Fix Push Notification Delivery Issue in React Native App – (Firebase/FCM, Node.js Backend)

Our production React Native app (iOS + Android) sends push notifications via Firebase Cloud Messaging (FCM), triggered from our Node.js backend. Notifications work reliably on Android, but on iOS they arrive inconsistently. Some users receive notifications with significant delays, while others do not receive them at all, particularly when the app is in a terminated (killed) state. We are looking for an experienced developer with strong knowledge of React Native, Firebase Cloud Messaging (FCM), Apple Push Notification Service (APNs), and iOS notification delivery behavior to diagnose and resolve the issue. The codebase is clean, and the problem appears to be well-scoped. We expect an experienced developer to: • Review the current push notification implementation • Investigate iOS notification delivery behavior and configuration • Verify APNs and Firebase settings • Check notification payload structure and delivery requirements • Identify the root cause of delayed or missing notifications • Implement and test the required fixes • Document the changes made and any recommendations for future reliability Required Skills: • React Native • Firebase Cloud Messaging (FCM) • Apple Push Notification Service (APNs) • iOS Push Notifications • Node.js • Mobile App Debugging Please describe relevant experience with iOS push notification troubleshooting and similar Firebase/APNs projects.