Why same fonts are showing different look on different roku devices?

I am working on bright script using scene graph. I have used fonts(Lato-Light, Lato-Regular and Lato-Bold) but these font shows different look (UI) in multiple roku devices. I have tested it in different roku devices(Roku-2, Roku-3, Roku-4 and Rock-stick). Font should be display same in all devices Please provide suggestion to resolve it.