Android Lint report <issue> duplication
Also you can run ./gradlew clean lintDebug so lint only analyze the debug build, in that way you increase the speed and you get only the warning for that build.Also you have to had in mind that if you use flavors the warnings could be reported by build type and also by flavor.
That message is just a warning, your application will still compile fine. It means that a either the children of your root element do not contain any children, or that the way you are organizing your layout can be more effectively done by using a flatter layout hierarchy. Ex. using one master FrameLayout, RelativeLayout, or LinearLayout instead of nesting layouts inside of each other.