I was having the same issue on all of my IOS simulators, tried multiple things:
but it didn't work.
The issue was with the FCM token for firebase push notifications. You wouldn't face this issue on any physical device , but if you have to work on the simulator than the solution that i figured was i commented out:
final fCMToken = await FirebaseMessaging.instance.getToken();
After this i stopped having the issue so i did all the work on the simulator and when i had to push out the build i enabled it again and it was working fine on the physical device.