Slow start onResume the application from the navigation button on real device?

Question

While testing my application on a real device, it works fine onStart, but onPause application to open another one, the application doesn't react well on click to resume the application again, in the screenshot below . It is late for 1 second and starts again. Then, the RecyclerView in fragment reloads everytime i start the application. If anyone can help, thank you.

Navigate to mobile apps

ChatListFragment.kt

class ChatListFragment : Fragment() {
    private lateinit var binding: FragmentChatListBinding
    private var chatList = ArrayList<Chats>()
    private var user: Chats?= null
    private var chatListAdapter = ChatListAdapter(chatList)
    private lateinit var auth: FirebaseAuth
    private lateinit var storage: FirebaseStorage
    private lateinit var firestore: FirebaseFirestore

    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        // Inflate the layout for this fragment
        val view =  inflater.inflate(R.layout.fragment_chat_list, container, false)
        binding = FragmentChatListBinding.inflate(layoutInflater)
        init()
        addContacts()
        changeListener()
        // Calling the override functions from
        // the Linear Layout Manager inner class
        val myLinearLayoutManager = object : LinearLayoutManager(context) {
            override fun canScrollVertically(): Boolean {
                return false
            }
        }
        view.popChatsRec.layoutManager = myLinearLayoutManager
        view.popChatsRec.adapter = chatListAdapter
        chatList.clear()
        return view
    }
    private fun addContacts(){
        val firebaseUser = auth.currentUser
        if (firebaseUser != null){
            firestore.collection("Contacts").document(auth.currentUser?.uid!!).collection("rooms").get()
                .addOnSuccessListener {
                    if (!it.isEmpty){
                        for (documents in it.documents){
                            val uId = documents.data?.get("uId").toString()
                            val uName = documents.data?.get("fullName").toString()
                            val uNum = documents.data?.get("fullNum").toString()
                            val uStatus = documents.data?.get("status").toString()
                            val uPresence = documents.data?.get("presence").toString()
                            val uImg = documents.data?.get("image").toString()
                            chatList.add(Chats(uId, uImg, uName, "", uNum, uStatus, uPresence))
                        }
                    } else {
                        Toast.makeText(context, "FailedHere", Toast.LENGTH_SHORT).show()
                    }
                    chatListAdapter.notifyDataSetChanged()
                }.addOnFailureListener { Toast.makeText(context, "FailureOverall", Toast.LENGTH_SHORT).show() }
        } else{
            Toast.makeText(context, "Null", Toast.LENGTH_SHORT).show()
        }
    }
    private fun changeListener(){
        firestore.collection("Contacts").document(auth.currentUser?.uid!!).collection("rooms")
            .addSnapshotListener { snapshots, e->
            if (e != null){
                Log.w(ContentValues.TAG, "listen:error", e)
                return@addSnapshotListener
            }
            for (dc in snapshots!!.documentChanges) {
                if (dc.type == DocumentChange.Type.MODIFIED) {
                    chatList.clear()
                    addContacts()
                    Log.d(ContentValues.TAG, "New city: ${dc.document.data}")
                }
            }
        }
    }
    private fun init(){
        auth = FirebaseAuth.getInstance()
        storage = FirebaseStorage.getInstance()
        firestore = Firebase.firestore
    }
}