Kotlin Observable.from is not waiting for observable

rxAndroid.java

// 1st Try
Observable.zip<Unit, Long, Unit>(Observable.from(units), Observable.interval(5, TimeUnit.SECONDS)) { unit, t -> unit }
            .subscribe({ unit ->
              // execute bluetooth and wait for response with .onBackpressureBuffer() and .timeout in seconds
              rxBluetoothService.sendAndReceiveWithTimeout("at+...", 10)
                        .subscribeOn(Schedulers.io())
                        .observeOn(AndroidSchedulers.mainThread())
                        .subscribe({ response -> 
                                   // do some stuff here
                         }, { 
                          //Handle error 
                        })
            })

             
//2nd Try
Observable.just(units)
    .concatMap({unitsList -> Observable.from(unitsList)})
    .observeOn(AndroidSchedulers.mainThread())
    .subscribeOn(Schedulers.computation())
    .timeout(11, TimeUnit.SECONDS)
    .flatMap({unit -> readBrakeValueFrom(unit, units, unitsMap).onErrorResumeNext(Observable.empty())})
    .subscribe() 
              
private fun readValuesFromBt(command: String) : Observable<String>{
        return rxBluetoothService.sendAndReceiveWithTimeout("at+...", 10)
                .observeOn(AndroidSchedulers.mainThread())
                .doOnNext { btwiResponse ->
                  // same maging
                }
                .onErrorReturn({""})
    }