LivePagedList emitting empty list

Question

I am using a paging library from Android Architecture Components.

Paging is implemented using ItemKeyedDataSource

class MyDatasource(
    private val queryMap: HashMap<String, String>) : ItemKeyedDataSource<String, Order>() {

    private val compositeDisposable: CompositeDisposable by lazy { CompositeDisposable() }

    override fun loadInitial(params: LoadInitialParams<String>, callback: LoadInitialCallback<Order>) {
        compositeDisposable.add(
            MyService.getService().fetchData(queryMap)
                .subscribeOn(Schedulers.io())
                .observeOn(AndroidSchedulers.mainThread())
                .subscribeWith(object : DisposableObserver<OrdersResponse>() {
                    override fun onNext(orders: OrdersResponse) {
                        callback.onResult(orders.data)
                    }

                    override fun onError(e: Throwable) {
                        e.printStackTrace()
                    }

                    override fun onComplete() {

                    }
                })
        )
    }

    override fun loadBefore(params: LoadParams<String>, callback: LoadCallback<Order>) {
        // do nothing
    }

    override fun loadAfter(params: LoadParams<String>, callback: LoadCallback<Order>) {
        queryMap["offsetOrderId"] = params.key

        compositeDisposable.add(
            MyService.getService().fetchData(queryMap)
                .subscribeOn(Schedulers.io())
                .observeOn(AndroidSchedulers.mainThread())
                .subscribeWith(object : DisposableObserver<OrdersResponse>() {
                    override fun onNext(orders: OrdersResponse) {
                        callback.onResult(orders.data)
                    }

                    override fun onError(e: Throwable) {
                    }

                    override fun onComplete() {
                    }
                })
        )
    }

    override fun getKey(item: Order): String {
        return item.orderId
    }
}

I build pagedlist in my viewmodel

class MyViewModel() : ViewModel() {
    private var myPagingConfig: PagedList.Config? = null

    var dataList: LiveData<PagedList<Order>>? = null

    fun getOrders(params: HashMap<String, String>) {


        if (myPagingConfig == null) {
            myPagingConfig = PagedList.Config.Builder()
                .setPageSize(LIMIT)
                .setPrefetchDistance(10)
                .setEnablePlaceholders(false)
                .build()
        }

        dataList = LivePagedListBuilder(MyDataFactory(
            MyDatasource(params)), myPagingConfig!!)
            .setInitialLoadKey(null)
            .setFetchExecutor(Executors.newFixedThreadPool(5))
            .build()
    }
}

However, when I observe the dataList in my activity, it sometimes (most of the times) returns an empty list, while in logcat I see that I had fetched data successfully. callback.onResult is invoked after it returns an empty list, but observer never gets notified again.

Can you tell me if what would cause this?