didReceiveRemoteNotification:fetchCompletionHandler not being called when app is in background and not connected to Xcode

There could be number of things might have gone wrong, The first from my own experience. In order to make silent push notification work. Your payload has to be structured correctly,

{
    "aps" : {
        "content-available" : 1
    },
    "data-id" : 345
}

Does your push message has content-available: 1 if not then iOS will not call the new delegate method.

- (void) application:(UIApplication *)application didReceiveRemoteNotification:(NSDictionary *)userInfo fetchCompletionHandler:(void (^)(UIBackgroundFetchResult))completionHandler