Depending on the version you have you might experience a blank screen. Force quit / close the app and re-open and that will fix it for most users.
If you are in a place with barely any cell signal or poor coverage, there's a chance you will face this if there are regulation or image updates pending and trying to download. This will be fixed in a future version. It's always best check for the latest regulations before going on a fishing trip with little to no cell signal, to ensure you have the latest regulation data.