Push Notifications getting dropped in iOS randomly

I am working on an iOS application built using React-Native and used OneSingnal for PushNotifications. Recently I upgraded to react-native version 0.61.5 and a compatible version of OneSingnal SDK (v3.6.4) along with that.

However, more often than not notifications get dropped somewhere in the middle and not reach mobile app. Here is what I know:

1. Devices are properly registered on OneSingal and I can see it in theAudience tab after I register.
2. Status of notifications is delivered in OneSingal. That is, it has been successfully sent to APNs servers.
3. Sometimes notifications do get received. So, the problem with mobile app code also seems unlikely.

Here is a scenario that I tried:

I uninstalled the app and installed the latest version at around 11.40 AM today. Logged in my account, set time for notification to be 12:00 PM (there is a setting in the app to set the time to receive notifications). Then I closed the app by swiping it out of app list by the double pressing home screen. But did not receive a notification at 12:00 PM. OneSingla showed delivered.

Then I opened the app again, used it for some time and set time for 2:00 PM again. This time I received the notification.

I am not really sure where can the problem be.