When there are multiple Canvases in root Canvas with "CanvasScaler", some child Canvas's RectTransform are broken. 1. Put a root Canvas (named as Root) with CanvasScaler (UI Scale Mode: Constant Pixel Size, Scale Factor: 2, Reference Pixels Per Unit: 100). 2. Put two or multiple Canvases (Pixel Perfect: Inherit) which RectTransform is streched as Root Canvas' child. 3. Play, then one or some Canvas(es)' RectTransform streched mode are broken. As a result, the RectTransform is left-bottom mode.