There is no response from writeDescriptor() when used in a chain

Hey. I have encountered such a problem when no response comes from method writeDescriptor when used in a chain. Here is my code:

override fun connectDevice() {
        rxBleClient.scanBleDevices(scanSettings, scanFilter)
            .flatMap { scanResult -> scanResult.bleDevice.establishConnection(false) }
            .flatMapSingle {
                rxBleConnection = it
                it.discoverServices()
            }
            .flatMapSingle { obtainCharacteristics(it) }
            .flatMapCompletable {
                readCharacteristic = it.first
                writeCharacteristic = it.second

                writeDescriptor(it.first)
            }
            .andThen(Single.fromCallable { startConnection() })
            .flatMap { it }
            .subscribeBy(
                onSuccess = { setupAndObserveNotifications(readCharacteristic!!) },
                onError = { Timber.d("$it") }
            )
    }

My method writeDescriptor:

private fun writeDescriptor(readCharacteristic: BluetoothGattCharacteristic): Completable {
        val descriptor = readCharacteristic.getDescriptor(READ_CHARACTERISTIC_CONFIG)
        return rxBleConnection!!.writeDescriptor(descriptor, BluetoothGattDescriptor.ENABLE_NOTIFICATION_VALUE)
            .doOnComplete { Timber.d("Descriptor wrote.") }
            .doOnError { Timber.e("Error while descriptor is writing: $it") }
    }

The chain comes to writeDescriptor(it.first), also called doOnComplete { Timber.d("Descriptor wrote."), but it does not go further down the chain in andThen(Single.fromCallable { startConnection() }) and next in subscribe. What could be the problem?

P.S. I reproduced the same example with the chain separately (without the library) withflatMapCompletable, andThen and etc., and everything was done correctly.

fun main() {
    Single.just(1)
        .delay(1, TimeUnit.SECONDS)
        .flatMapCompletable { getCompletable() }
        .andThen(Single.fromCallable { getSingle() })
        .flatMap { it }
        .subscribe { i -> println(i) }

    Thread.sleep(5000)
}

private fun getCompletable(): Completable {
    return Completable.fromRunnable {
        Thread.sleep(1000)
    }
}

private fun getSingle(): Single<Int> {
    return Single.just(5)
}

In the console comes the correct answer - 5

[dariuszseweryn]

.establishConnection() does not complete on its own. You can read about it in the Observable behaviour part of Readme

[akhbulatov]

Ok, thanks.