Photo's Doesn't Always Add To PhotoStream (On iPad) not on Mac

Hi,

So i have setup the settings on my iPad, to whenever i take a photo, the camera deposits the photos in the camera roll as normal, and then automatically gets added to the photo stream, however some photos by the look of it, the most recent photos have not added to the photo stream, please can you tell me why this is.

As a side not the iPad is connect to WIFI.

Is there a fix for this, if so how please?