There can be many reasons for notifications to not being received. And one would need a lot more details on what is being sent, what is the actual state of the devices, etc., for a meaningful answer as to what could be wrong:
- you might have an incorrect token for the user
- the push payload might be incorrect or otherwise malformed for certain pushes
- the users might have inadvertently turned off your notifications, silenced them, or sent them to daily summaries
- you are sending silent or low priority pushes that are being throttled
If you can share the apns-id of a notification which did not make it to the user (a recent one, within the last couple days, and also share the time and time zone sent), we can take a look to see if the push was delivered at all.