React-Router 4 catch all route

Not sure if this will work for you as I have some 3rd party babel wrappers in use, but I get away with declaring all my routes then last putting

<Route path="/*" render={() => <SomeComponent /* possible prop injection */ />}/>

I've used this fairly frequently, but you can also use

<Route render={() => <SomeComponent />} />

I don't use this much as I prefer more landmarks in my code, but I got the above from https://tylermcginnis.com/react-router-handling-404-pages/

Try this implementation

const AppRouter = (props) => {
        return (
            <BrowserRouter>
                <div>
                    <Header />
                    <Switch>
                        <Route exact path="/" component={Landing} />
                        <Route path="/about" component={About} />
                        <Route path="/contact" component={Contact} />
                        <Route component={NotFoundPage} />
                    </Switch>
                    <Footer />
                </div>
            </BrowserRouter>
        );
    }