My app has FCM with message payload setup and works successfully using APNs Auth Key when running on Xcode debug mode and when downloading release build from TestFlight by testers. Both App Store ID and Team ID are set up correctly in Firebase project settings as well. However I found that if I install the old build app from AppStore first (this build has corresponding GoogleService-Info.plist but didn't have complete FCM functionalities implemented yet), and then update to new build which has complete FCM functionalities, the app can still get FCM token but doesn't seem to receive any FCM messages. If I use Firebase's Notification composer to send message with the token received, the app can actually receive that notification so this means the APN should be set correctly and the token is valid. I would like to know what may cause FCM on app works differently between "update from an old build" or "new install" from App Store, and how I could fix it?