Not sure if it's related but since updating to iOS 9 any image with transparency is just a black image
We have submitted an update fixing this problem on 9/11, but it is still under review at Apple. Hopefully, they will approve the app soon. Sorry for the inconvenience.
Still happening on a transient basis (possibly not enough RAM available when project is opened or saved?). Union v.1.5.4 iOS 9.3.4. iPad Pro 9.7"