This was a doozy to figure out!
In windowed builds, the uGUI input does not work on the right side of the screen. The area affected increases as the aspect ratio of the window increases.
I tracked the issue down to MultipleDisplayUtilities.RelativeMouseAtScaled which is used when raycasting to do coordinate scaling to compensate for multiple displays or something, but it seems to be scaling the mouse coordinates out of the camera’s viewport so raycasts return early even though the cursor is over the window.
I referenced some of the scaling math to visualize where the inputs become invalid in red. As you can see, clicking and hovering has no effect on the example buttons.
Bug report created at CASE IN-14210
