We have experienced the same behavior and have been trying to understand why iOS decides to deliver some notifications and not others. What we have worked out so far is: Messages will get received more reliably in background when on wifi than on cellular data. In fact, when on a cellular network (3g/4g), if your … Read more
Short answer, yes The exciting new opportunity for app developers in iOS 8 is that Apple will now deliver “silent” pushes even if the user has opted out of notifications. Also, “silent push” is no longer just for Newsstand apps. Every app can take advantage of this ability to refresh content in the background, creating … Read more
EDIT: While this answer is fully applicable, there are some additions (not changes) to notifications in iOS 12. I highly recommend watching WWDC 2018: What’s New in User Notifications and read this amazing and must read article. Main changes are: grouped notifications along with summary format provisional notifications ie show notifications directly in notification center … Read more