Disappear items if the list has one item in the nested RecyclerView

Question

Greating follow Coders, I would like to ask you, because I am stucked.

Currently I working on a following page, what is similar to Instagram's follow process. In my case the app will fitch first the followed people, how you follow. If it is done, the program will start the parent recyclerview and write out the name and the profilepicture of the followed user. The second step is to fetch the followed users trainings. Until that everything works fine, but in the most cases the first recyclerview (nested)in the parents recyclerview dissapear when it has just one training inside the list. The same happens if everything is loaded correctly at the first time, but when I scroll in the horizontal child recyclerview (at that time will be created the item's view, but already fetched from the cloud) the recyclerview dissapears always. Only the first one if it has only one item.

Is there any attribute of the recyclerview, what I have to set?

Thanks for your help. Peter Pázmándi

Parent onBindViewHolder (in a fragment)

override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, 
    savedInstanceState: Bundle? ): View?
{
    val rootView = inflater.inflate(R.layout.news_fragment, container,               
        false)

    firebaseViewModel = 
        ViewModelProviders.of(this).get(FirebaseViewModel::class.java)

    FirebaseRepository.currentUserId?.let {
        Log.i("$TAG.currentUserId", "${it}")
        firebaseViewModel.getFollowedWithLimit(it).observe(this, Observer { 
        list ->
            list?.let {
                loadedUsers = it.size
                for (i in 0..it.lastIndex)
                {
                    if(it[i].followingUsersLastTrainingTimeStamp != 0L)
                    {
                        wholeListOfFollowers.add(it[i].followingUserId)
                    }
                }
                Log.i("$TAG.wholeList", "$wholeListOfFollowers")

                rootView.recyclerView_newsfeed.apply {
                    recycledViewPool.setMaxRecycledViews(10,20)
                    layoutManager = CustomLinearLayoutManager(context!!, 
                        LinearLayoutManager.VERTICAL, false)
                    adapter = NewsFeedAdapter(context, wholeListOfFollowers)
                }

            }
        })
    }

    return rootView
}

Child onBindViewHolder

override fun onBindViewHolder(holder: NewsFeedViewHolder, position: Int)
{
    var userId = usersId[position]

    if(!fetchedUser.contains(position))
    {
        fetchedUser.put(position, true)

        firebaseViewModel.getTrainigs(userId).observe(context as 
        FragmentActivity, Observer {
            it?.let {trainigsList ->
                if(trainigsList.size != 0)
                {
                    firebaseViewModel.getUserByUserId(userId).observe(context, 
                    Observer {user ->
                        user?.let {
                            trainings = trainigsList.toMutableList()
                            loadedTrainingSize = trainings.size
                            if(!user.profileImageUrl.equals(""))
                            {
                                Picasso.get()
                                    .load(user.profileImageUrl)
                                    .into(holder.profileIamge)
                            }

                            holder.username.text = user.name

                            holder.childRecyclerView.apply {
                                recycledViewPool.setMaxRecycledViews(0,1)
                                layoutManager = 
                                  CustomLinearLayoutManager(context, 
                                      RecyclerView.HORIZONTAL, false)
                                adapter = TrainingItemAdapter(context, 
                                    trainings)
                                scrollToPosition(0)
                                stopScroll()
                            }
                        }
                    })
                }
                else
                {
                    Log.i("$TAG.size", "${it.size}")
                    holder.consraintLayout.visibility = View.GONE
                }
            }
        })
    }
    else
    {
        Log.i("$TAG.fetchedUser", "true")
    }
}