React-native-firebase: Push notifications not always working on iOS

I implemented an app in react-native that send push notifications via Firebase. Most of the time, it is working well, but sometimes, the push notifications are not received by the device (mostly iOS 13 devices).

For the devices receiving my push notifications correctly, onNotification is triggered everytime (foreground and background).

For the devices not receiving my push notifications, onMessage is triggered (only on foreground).

package.json

"react-native-firebase": "^5.6.0"

Podfile

pod 'Firebase/Core', '~> 6.19.0'
pod 'Firebase/Functions', '~> 6.19.0'
pod 'Firebase/Messaging', '~> 6.19.0'
pod 'Firebase/Auth', '~> 6.19.0'

To test out my push notifications, I am sending it via POSTMAN, using the firebase API, with the current Payload:

{
"to" : "my_FCM_token",
"priority" : "high",
"notification" : {
    "body" : "Body TEST",
    "title": "TEST Notification",
    "vibrate": 1,
    "sound": 1
},
"data" : {
    "key" : "value"
}
}

Note that it always returns me a success

AppDelegate.m

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    // FIREBASE CONFIG
    [FIRApp configure];

    // SETTING ROOT VIEW CONTROLLER
    RCTBridge *bridge = [[RCTBridge alloc] initWithDelegate:self launchOptions:launchOptions];
    RCTRootView *rootView = [[RCTRootView alloc] initWithBridge:bridge
                                               moduleName:@"MyModule"
                                        initialProperties:nil];
    self.window = [[UIWindow alloc] initWithFrame:[UIScreen mainScreen].bounds];
    UIViewController *rootViewController = [UIViewController new];
    rootViewController.view = rootView;
    self.window.rootViewController = rootViewController;
    [self.window makeKeyAndVisible];
    [RNSplashScreen show];
    return YES;
 }   

App.js

async componentDidMount() {

  firebase.messaging().hasPermission().then(enabled => {
    if (enabled) {
      firebase.messaging().getToken().then(token => {
        global.token = token;
      })
    } else {
      firebase.messaging().requestPermission()
        .then(() => {
          alert("Permission Accepted", error)
        })
        .catch(error => {
          alert("Permission Denied", error)
        });
     }
  });

  this.initialNotificationListener = firebase.notifications().getInitialNotification().then((notificationOpen: NotificationOpen) => {
    alert("Getting initial Notification")
  });

  this.notificationOpenedListener = firebase.notifications().onNotificationOpened((notificationOpen: NotificationOpen) => {
    alert("onNotificationOpened triggered")
  });

  this.notificationListener = firebase.notifications().onNotification((notification: Notification) => {
    alert("onNotification triggered")
  });

  this.onMessageListener = firebase.messaging().onMessage(async (remoteMessage) => {
    alert("onMessage triggered")
  });
}

componentWillUnmount() {
  this.notificationOpenedListener();
  this.notificationDisplayedListener();
  this.notificationListener();
  this.initialNotificationListener();
  this.onMessageListener();
}

Any help would be appreciated, thank you :)