Does Lit UI work on iOS?

Hi, I have a scene which uses a world space UI canvas. The UI elements all have a material that uses the UI / Lit / Bumped shader. There is a single point light illuminating the scene. On PC/Mac the scene looks fine -- a smooth gradient of lighting from the center of the point light, as you'd expect. But on iOS 90% of the UI is burned out with a circle of pure white leaving a small radial area at the edge that is working properly. Is there a problem with Lit UI on iOS or is something amiss with my scene? Cheers, --Sam