Angular 7 - catchError is not intercepting exceptions

Question

The catchError operator is not intercepting back-end errors. For example, in the back end I do an email check and return an exception if the email already exists, as below:

public Usuario insert(Usuario usuario) {
    if (usuarioService.findByEmail(usuario.getEmail()) == null) {
        usuario = getRepository().save(usuario);
        return usuario;
    }else {
        throw new DataIntegrityException("Email já está em uso");
    }
}

However, on the front end in Angular 7, in my service method, the exception is not intercepted and the application redirects me to the main screen, preventing a proper handling and feedback of the error. Follows service code:

@Injectable
export class UsuarioService{

url: string = `${API_CONFIG.baseUrl}/usuarios`;

usuariosChanged = new EventEmitter<Observable<Usuario[]>>();

constructor(private http: HttpClient){
}

findAll(): Observable<Usuario[]>{
    return this.http.get<Usuario[]>(${this.url});
}

findById(id: number): Observable<Usuario>{
    return this.http.get<Usuario>(`${this.url}/id/${id}`);
}

post(usuario: Usuario): Observable<Usuario>{
    return this.http.post<Usuario>(this.url, usuario)
        .pipe(
            tap(data => this.usuariosChanged.emit(this.findAll())),
            catchError(this.handleError))
}

private handleError(error: any) {
    let erro = error.message || 'Server error';
    console.error('Ocorreu um erro', error);
    return Observable.throw(erro);
}
}

And excerpt from the Component:

onSave(){
     this.usuarioService.post(this.form.value)
        .subscribe(data => {
           this.notificationService.notify("Usuário salvo com sucesso!");
        },
        error => { 
           alert("Ocorreu um erro ao salvar!");
        });
}

I still have an Httpinterceptor. My requests go through it, but if they are in error, they are not captured by the catcher either. Follows the code of the Interceptor:

@Injectable()
export class ErrorInterceptor implements HttpInterceptor{

constructor(){
}

intercept(req: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>>{
    return next.handle(req).pipe(catchError(err => {
        const error = err.error.message || err.statusText;
        return throwError(error);
    }))
}
}

export const ErrorInterceptorProvider = {
   provide : HTTP_INTERCEPTORS,
    useClass: ErrorInterceptor,
   multi: true,
};