Não consigo descobrir por que isso está acontecendo. Nenhum dos retornos de chamada rx (onCompleted (), onError (), onNext ()) não é acionado pela minha chamada. A única coisa que recebo é esta saída okhttp:

D/OkHttp: --> GET https://api.privatbank.ua/p24api/exchange_rates?json=true&date=20.11.2016 http/1.1
D/OkHttp: --> END GET
D/OkHttp: <-- HTTP FAILED: java.io.IOException: Canceled

Módulo de atualização:

@Module
public class RestModule {

    @Provides
    @Singleton
    public HttpLoggingInterceptor providesHttpLogginInterceptor() {
        return new HttpLoggingInterceptor().setLevel(HttpLoggingInterceptor.Level.BODY);
    }

    @Provides
    @Singleton
    public OkHttpClient providesOkHttpClient(@NonNull HttpLoggingInterceptor loggingInterceptor) {
        return new OkHttpClient.Builder()
            .addInterceptor(loggingInterceptor)
            .connectTimeout(ConstantsManager.CONNECTION_TIME_OUT, TimeUnit.SECONDS)
            .readTimeout(ConstantsManager.READ_TIME_OUT, TimeUnit.SECONDS)
            .build();
    }

    @Provides
    @Singleton
    public Gson providesGson() {
        return new GsonBuilder().create();
    }

    @Provides
    @Singleton
    public Retrofit providesRetrofit(@NonNull OkHttpClient okHttpClient, @NonNull Gson gson) {
        return new Retrofit.Builder()
            .baseUrl(ConstantsManager.BASE_URL)
            .client(okHttpClient)
            .addConverterFactory(SimpleXmlConverterFactory.create())
            .addConverterFactory(GsonConverterFactory.create(gson))
            .addCallAdapterFactory(RxJavaCallAdapterFactory.create())
            .build();
    }

    @Provides
    @Singleton
    public PrivatbankApi providesPrivatbankApi(@NonNull Retrofit retrofit) {
        return retrofit.create(PrivatbankApi.class);
    }
}

Interface da API:

public interface PrivatbankApi {

    @GET
    Observable<CurrentRates> loadCurrentRates(@NonNull @Url String url);

    @GET("exchange_rates")
    Observable<DateRates> loadDateRates(@NonNull @Query("json") Boolean json, @NonNull @Query("date") String date);

}

Inscrição:

subscription = dataManager.loadDateRates(date)
                .subscribeOn(Schedulers.io())
                .doAfterTerminate(() -> {
                })
                .subscribe(dateRates -> {
                    // My code here...
                }, throwable -> {
                    Timber.e(throwable, "Error while loading data occurred!");
                });

A propósito, as duas chamadas recebem o mesmo erro:

D/OkHttp: --> GET https://privat24.privatbank.ua/p24/accountorder?oper=prp&PUREXML&apicour&country=ua http/1.1
D/OkHttp: --> END GET
D/OkHttp: <-- HTTP FAILED: java.io.IOException: Canceled
D/OkHttp: --> GET https://api.privatbank.ua/p24api/exchange_rates?json=true&date=20.11.2016 http/1.1
D/OkHttp: --> END GET
D/OkHttp: <-- HTTP FAILED: java.io.IOException: Canceled