Collection background image uploading, not loading on test app

I have my top level collection of my test app with a working background image. I am trying to add a background image to another collection in my app, and it will save, upload and publish - however even having done the update each time, the background still stays white. Going back into the collection settings, the background image I made is uploaded and appears correctly but is absent from the app.

I tried uploading an image with the size necessary for the iPhone, I tried uploading one with the 2048 dimensions, and I tried uploading the image I used for my first background at top level which is still working - but none have appeared on my app.

Is there a bug in the system for this? Is there another way of working the background image that I am not aware of or has been updated in Digital Publishing Suite?