Breaks compilation on API 29

My app (androidx) wont compile any more ... I get

Session 'app': Installation did not succeed.
			The application could not be installed: INSTALL_FAILED_UPDATE_INCOMPATIBLE
			Retry

and 

Error running 'app': Default Activity not found

I have specified xmlns:app="http://schemas.android.com/apk/res-auto"
in my nested-scroll-view layout