Why is the first Fragment in Tablayout loaded only after clicking on the 3rd and further tabs?

Question

Android

I have a Tablayout with 6 days of the week tabs. Each tab has a RecyclerView of the list of items. The first time it appears in the first tab, only the first item in the list is displayed. The first element is simple, followed by classes. When switching to the 3rd tab and returning to the first, all elements are displayed correctly. Probably a problem with the RecyclerView. What should I do to make it work correctly? Thanks in advance!
PageAdapter.java

package com.example.schedule;
import android.content.Context;
import androidx.annotation.NonNull;
import androidx.fragment.app.Fragment;
import androidx.fragment.app.FragmentManager;
import androidx.fragment.app.FragmentStatePagerAdapter;

public class PageAdapter extends FragmentStatePagerAdapter {
    final int PAGE_COUNT = 6;
    private String tabTitles[] = new String[] { "Пн", "Вт", "Ср", "Чт", "Пт", "Сб"};
    private Context context;

    public PageAdapter(@NonNull FragmentManager fm, Context context) {
        super(fm);
        this.context = context;
    }
    @NonNull
    @Override
    public Fragment getItem(int position) {
        return PageFragment.newInstance(position + 1);
    }

    @Override
    public int getCount() {
        return PAGE_COUNT;
    }
    @Override public CharSequence getPageTitle(int position) {
        // генерируем заголовок в зависимости от позиции
        return tabTitles[position];
    }
}

PageFragment.java

package com.example.schedule;

import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

import androidx.annotation.NonNull;
import androidx.fragment.app.Fragment;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;
import com.example.schedule.utils.RecyclerTable;

public class PageFragment extends Fragment {
    public static final String ARG_PAGE = "ARG_PAGE";

    private int mPage;
    RecyclerView recyclerView;
    static String str="";

    public static PageFragment newInstance(int page) {
        Bundle args = new Bundle();
        args.putInt(ARG_PAGE, page);
        PageFragment fragment = new PageFragment();
        fragment.setArguments(args);
        return fragment;
    }

    @Override public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        if (getArguments() != null) {
            mPage = getArguments().getInt(ARG_PAGE);
        }
    }

    @Override public View onCreateView(@NonNull LayoutInflater inflater, ViewGroup container,
                                       Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment_page, container, false);
        recyclerView = (RecyclerView) view.findViewById(R.id.tablelist);
        recyclerView.setLayoutManager(new LinearLayoutManager(getActivity()));
        recyclerView.setHasFixedSize(true);
        switch (mPage){
            case 1: Table.Week = Table.Mnd; break;
            case 2: Table.Week = Table.Tue; break;
            case 3: Table.Week = Table.Wed; break;
            case 4: Table.Week = Table.Th; break;
            case 5: Table.Week = Table.Fri; break;
            case 6: Table.Week = Table.Sat; break;
        }
        RecyclerTable tableAdapter = new RecyclerTable(Table.Week, Table.Week.size());
        recyclerView.setAdapter(tableAdapter);
        return view;
    }
}

RecyclerTable.java

package com.example.schedule.utils;

import android.text.Html;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

import androidx.annotation.NonNull;
import androidx.recyclerview.widget.RecyclerView;

import com.example.schedule.Lesson;
import com.example.schedule.R;

import java.util.ArrayList;

public class RecyclerTable extends RecyclerView.Adapter<RecyclerTable.TableViewHolder>{
    ArrayList<Lesson> Lesson;
    int i;
    public RecyclerTable(ArrayList<Lesson> Lesson, int i){
        this.Lesson = Lesson;
        this.i = i;

    }
    @NonNull
    @Override
    public TableViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.table, parent, false);
        return new TableViewHolder(view);
    }

    @Override
    public void onBindViewHolder(@NonNull TableViewHolder holder, int position) {
        //if(i!=0) {
            holder.textTime.setText("Время");
            //holder.textLesson.setText("Ghtlvtn");
            holder.textLesson.setText(Html.fromHtml(Lesson.get(position).getFull_name_lesson()));
            holder.textKorpus.setText(Lesson.get(position).getStation());
            //Log.i("myTag","Set text on position " + position);
        //}
    }

    @Override
    public int getItemCount() {
        return i;
    }

    //////////////////////////////////////////////////////
    public class TableViewHolder extends RecyclerView.ViewHolder{
        TextView textTime;
        TextView textLesson;
        TextView textKorpus;

        public TableViewHolder(@NonNull View itemView) {
            super(itemView);
            textTime = (TextView) itemView.findViewById(R.id.textTime);
            textLesson = (TextView) itemView.findViewById(R.id.textLesson);
            textKorpus = (TextView) itemView.findViewById(R.id.textKorpus);
        }

    }
   ///////////////////////////////////////////////////////////

    public  static ArrayList<Lesson> NewLesson(ArrayList<Lesson> Lesson){
        Log.i("MyTagAboutSize","Size Array: " + Lesson.size());
        return Lesson;
    }
}

Lesson.java

package com.example.schedule;

import android.util.Log;

public class Lesson {
    private String subgroup = "";
    private String   name_lesson = "";
    private String type_lesson = "";
    private String   building = "";
    private String room = "";
    private String   Family = "";
    private String   Name = "";
    private String   Secondname = "";
    private String special = "";

    private String full_name_lesson;
    private String station;

    private int day;
    private int number;

    public Lesson(String subgroup,String   name_lesson, String special,
                  String type_lesson,String   building,
                  String room,String   Family,String   Name, String   Secondname, int day, int number){

        this.name_lesson = name_lesson + " ";

        if(!special.equals("")){
            this.special = "(" + special + ") ";
        }
        if(subgroup.equals("0"))
            this.subgroup = "";
        else
            this.subgroup = "подгруппа " + subgroup;

        if(!type_lesson.equals(""))
            this.type_lesson = "(" + type_lesson + ")";
        if(building.equals("0"))
            this.building = "";
        else
            this.building = "Корпус " + building + "\n";

        if(!room.equals("ДОТ")&&!room.equals(""))
        this.room = "ауд" + room;
        this.Family = Family + " \n";

        if(!Name.equals(""))
            this.Name = Name.charAt(0) + ". ";
        if(!Secondname.equals(""))
            this.Secondname = Secondname.charAt(0) + ".";

        this.day = day;
        this.number = number;

            //Log.i("myTag","Lesson add " + name_lesson);

        full_name_lesson = "<b>" + this.name_lesson + "</b> " + this.special + this.type_lesson + "\n<b>" + this.Family + this.Name + this.Secondname + "</b>\n"+ this.subgroup;
        station = this.building + this.room;

            //Log.i("myTag","Full name " + full_name_lesson + "\nstation " + station);
    }

    public String getFull_name_lesson(){
        return full_name_lesson;
    }

    public  String getStation(){
        return station;
    }

    public int getDay(){ return day; }

    public  int getNumber(){ return number; }
}

Table.java

Link to Habr: https://github.com/AnnaDesert/Schedule1.0
Since I can fit everything

Answer 1

In general, your problem is in asynchronous data loading and in statics.
Everything happens like this: you go to the screen, the adapter is created instantly and filled from Mnd. The data there is 1 element. Then the data is loaded, the static is updated, but no one notifies the adapter about this (notify*). Then you start walking through other pages, at some point you return, and voila, you create a new adapter with fresh data.
What to do. Repository pattern and Observer pattern (or spin RxJava). No static nafig. You will immediately have to think about what you are doing, it will be difficult at first, but it is necessary. Throw out the asynctask and forget about it like a bad dream. retrofit+okhttp+moshi. No parsing by json, especially on the main thread.