Progress bar causes black screen on iOS

When using a progress bar that is partly filled the screen on an iOS device will be blacked out except for the screen space containing the filled part of the progress bar

This did not occur in standalone game.

1. Download the attached file
2. Open the project
3. Launch on to iOS

Result: The screen will turn all black except for the filled area of the progress bar
Expected: The progress bar would be slightly filled and the rest of the level would be visible

UMG Progress bar iPhone causes black screen