As you're specific about the three devices, it sounds a little odd and Bogdan Andresyuk idea of reseting those devices would make sense.
I've had issues in the past whereby some push notifications are not delivered. Can I ask are you sending notifications outin order i.e. are these three devices the last three devices that you try and send notifications too? or is there a sequence or some sort of pattern that you can build. Say you have 10 devices and three don't get the notification and the notifications are sent in order and it's device 3, 6 and 9 that don't get the messages.
If there is something like this then it could well be your push notifications are being rejected by Apple. Perhaps because you're opening and closing a socket to the APNS to many times in quick succession. Apple doesn't like this and prefers you hold the socket open why you send your notifications.
If not then perhaps you could provide a little more detail about the devices and the sequence of events and how you're set up your push service. I use urban airship as the take care of the sockets etc for you and you can send 1 million for free.
