If a Custom Renderer is added to a Xamarin Forms Android project and suddenly the application crashes before loading the first screen then do a rebuild or clean of the Android project and re-run.
A common pitfall I see in Xamarin Forms is adding a Loading page icon for every page. This is one of the problems that plagued the current Home Control Flex application. Instead of having to loading icon on each page you can crate a base page that has a loading screen on each. You can do this using the ContentPropertyAttribute on your base page as shown below.