Silent push message, can´t react if app is in background and unplugged

I am trying to react on silent push messages. I registered my app for the two background modes in my plist file.

I am sending the following json to my app:

{
"aps": {
     "content-available": 1
},
"Bla": "Blub"
}

If my app is in foreground, everything works. As I am receiving the push I execute a function in my code. If my app is in background and plugged to my Mac or ac, everythings fine as well... But if I unplug my device, the device is not getting or at least my function is not called anymore...Why is that?