Why do Push notifications not always work?

[blast87]

Myself and friends notice push notifications for a lot of apps don't always work. For example, the Facebook app will sometimes show notifications and the number count on the app, but other times won't. Only when you open the app will the notifications appear. Is this an iOS bug? Developer fault? Users fault that I can fix somehow? Or somewhere in between?
Some other apps I notice it in quora, Instagram, Facebook messenger, words w friends, amongst others.

 

[alice04]

Myself and friends notice push notifications for a lot of apps don't always work. For example, the Facebook app will sometimes show notifications and the number count on the app, but other times won't. Only when you open the app will the notifications appear. Is this an iOS bug? Developer fault? Users fault that I can fix somehow? Or somewhere in between?
Some other apps I notice it in quora, Instagram, Facebook messenger, words w friends, amongst others.

Not only you and your friends, including me and my friends as well. hahaha. I think it's FB thats having issues

 

[darricksailo]

If you are on an iDevice without cellular network, I think push notifications stop working when your wifi gets disabled (when it's not plugged into the charger)

I think wifi gets periodically re-enabled to check for push notifications. How often it does that, I'm not sure