I want the phone to vibrate more than once on incoming push notifications.
To realize this behavior I scheduled several text-less local notifications (after 1 second, 2 seconds, ...) in the application:didReceiveRemoteNotification:fetchCompletionHandler: method.
This works well on the device that I use for development and several other phones, but it doesn't work on all of them.
What can I do to make it work on all devices?
Since iOS looks a how you app handles application:didReceiveRemoteNotification:fetchCompletionHandler: it may or may not call that method. If a user has disabled background updating then the method is never called.
Since you are misusing this API for something it is not intended there will be no way to make work on all devices.