APNS failure rate

Hi guys,
Wonder if anyone could help me please and share some of your experience with APNS.
We have built a silent push notification service which pushes a message to the apps depending on a trigger of our backend.
Our backend uses the Firebase APIs to send the notifications and we have discovered that in Android we have a failure rate of about 2% and in iOS we have a failure rate of about 10%
On both platforms we are following the firebase recommended ways of managing the FCM tokens and we are fairly confident that it's not an app FCM token management issue as we have reviewed it multiple times.
Despite both platforms are using the same backend and the same Firebase APIs, as we know, iOS will be also dependant on the Apple Push Notification Service and make us wonder if this big discrepancy on the failure rate might be expected from APNS.
So question out there to anyone that can help is:
From your experience have you found APNS or using Firebase Push Notifications APIs on iOS to have a considerable failure rate? And if yes do you have some numbers on those rates?
Many many thanks and good coding,
Miguel Santos