Why does getting the speed in my android app fluctuate too high even when not moving while in the app "GPS Test" it shows 0?

Question

The speed can jump even to 70km/h, I've never had such jumps before. I think it's related to poor reception, but still, the other app works fine, Maybe they filter out wrong data or they use a different way to get location? This is the code I'm using in a foreground service:

override fun onCreate() {
    super.onCreate()
    mHandlerThread.start()
    mBroadcastManager = LocalBroadcastManager.getInstance(this)
    createNotificationChanel()
    requestLocationUpdates()
}
@SuppressLint("MissingPermission")
@Synchronized private fun requestLocationUpdates() {
    mFusedLocationClient = LocationServices.getFusedLocationProviderClient(this)
    createLocationRequest()
    val locationCallback: LocationCallback?
    locationCallback = object : LocationCallback() {
        @Synchronized override fun onLocationResult(locationResult: LocationResult) {
                val location = locationResult.lastLocation
                val speedKmph = ((location?.speed?: 0f) * 3.6).roundToInt()
                mSpeed = speedKmph
        }
    }
    mFusedLocationClient.requestLocationUpdates(
        mLocationRequest,
        locationCallback,
        mHandlerThread.looper
    )
}
@Synchronized   private fun createLocationRequest() {
 LocationRequest.Builder(Priority.PRIORITY_HIGH_ACCURACY, 1000)
 .setWaitForAccurateLocation(false)
 .setMinUpdateIntervalMillis(500)
 .build().also { mLocationRequest = it }
}

Answer 1

GPS data is naturally noisy and is normally filtered with a Kalman filter or something similar. Different GPS receivers apply different amounts of filtering, and apps can apply their own additional filtering.