Why is the layout displayed in the fragment only on the first call?

Question

Android

Hello everyone, I'm using Navigation Drawer Activity at the same time as Tabbed Activity (created personally via SimpleFragmentPageAdapter).
Main Activity is used only once, and everything else is displayed in fragments (android studio 3.5.3, defaul templates)
So, when opening a fragment for the first time, all the information is in place as in the image:

Then we exit the fragment by going to another fragment and when opening fragment again, the information is completely missing, and you can’t switch between tabs (the position of the scroll bar can be in the center)



SimpleFragmentPagerAdapter

public class SimpleFragmentPagerAdapter extends FragmentPagerAdapter {
    final int PAGE_COUNT = 2;
    private Context mContext;

    public SimpleFragmentPagerAdapter(FragmentManager fm, Context context) {
        super(fm);
        mContext = context;
    }

    @Override
    public Fragment getItem(int position) {
        switch (position) {
            case 0:
                MileageCalcFragment fragment1 = new MileageCalcFragment();
                return fragment1;

            case 1:
                PaybackCalcFragment fragment2 = new PaybackCalcFragment();
                return fragment2;
            default:
                MileageCalcFragment fragment3 = new MileageCalcFragment();
                return fragment3;
        }
    }

    @Override
    public int getCount() {
        return PAGE_COUNT;
    }

    @Override
    public CharSequence getPageTitle(int position) {
        final String mileageCalc = mContext.getResources().getString(R.string.mileage_calculator);
        final String paybackCalc = mContext.getResources().getString(R.string.payback_calculator);
        final String[] tabTitles = {mileageCalc, paybackCalc};
        return tabTitles[position];
    }
}

MileageCalcFragment

public class MileageCalcFragment extends Fragment implements View.OnClickListener {

    private CalcViewModel calcViewModel;
    private ImageButton chooseCar;
    private ImageButton chooseVan;
    private ImageButton chooseTruck;
    private Button calculateMileage;
    private EditText getChargeAmount;
    private TextView resultMileageCalc;
    private int cartype;
    private double total;
    private double summ;
    private static final double[] fuelPrices = {0.70 /*CNG*/, 1.76 /*Diesel*/, 1.76 /*AI95*/, 1.66 /*AI92*/, 0.93 /*SUG*/};

    public MileageCalcFragment() {
        // Required empty public constructor
    }


    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        calcViewModel =
                ViewModelProviders.of(this).get(CalcViewModel.class);
        View root = inflater.inflate(R.layout.fragment_mileage_calc, container, false);

        chooseCar = root.findViewById(R.id.chooseCar);
        chooseVan = root.findViewById(R.id.chooseVan);
        chooseTruck = root.findViewById(R.id.chooseTruck);
        getChargeAmount = root.findViewById(R.id.getChargeAmount);
        resultMileageCalc = root.findViewById(R.id.resultMileageCalc);

        chooseCar.setOnClickListener(this);
        chooseVan.setOnClickListener(this);
        chooseTruck.setOnClickListener(this);

        calculateMileage = root.findViewById(R.id.calculateMileage);
        calculateMileage.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                resultMileageCalc.setText(Double.toString(total + 100));

                Toast.makeText(getActivity().getApplicationContext(), "Cho", Toast.LENGTH_SHORT).show();
            }
        });

        return root;
    }


    @Override
    public void onClick(View view) {
        switch (cartype) {
            case R.id.chooseCar:
                chooseCar.getBackground().setAlpha(100);
                chooseVan.setBackgroundResource(R.drawable.imageview_red_border);
                final double[] carFuelRates = {8.7 /*CNG*/, 5.7 /*Diesel*/, 8.1 /*AI95*/, 8.1 /*AI92*/, 10.4 /*SUG*/};
                if (getChargeAmount.getText() == null) {
                    summ = Double.parseDouble(getChargeAmount.getText().toString());
                } else {
                    Toast.makeText(getActivity().getApplicationContext(), "The planned amount of fuel should be the number", Toast.LENGTH_LONG).show();
                }
                for (int i = 0; i <= 5; i++) {
                    double[] resArray = new double[5];
                    resArray[i] = ((summ * 100) / (carFuelRates[i] * fuelPrices[i]));
                    total = total + ((summ * 100) / (carFuelRates[i] * fuelPrices[i]));
                }
                break;
            case R.id.chooseVan:
                chooseVan.getBackground().setAlpha(100);
                chooseVan.setBackgroundResource(R.drawable.imageview_red_border);
                final double[] vanFuelRates = {18 /*CNG*/, 11.5 /*Diesel*/, 16 /*AI95*/, 16 /*AI92*/, 19.2 /*SUG*/};
                if (getChargeAmount.getText() == null) {
                    summ = Double.parseDouble(getChargeAmount.getText().toString());
                } else {
                    Toast.makeText(getActivity().getApplicationContext(), "The planned amount of fuel should be the number", Toast.LENGTH_LONG).show();
                }
                for (int i = 0; i <= 5; i++) {
                    double[] resArray = new double[5];
                    resArray[i] = ((summ * 100) / (vanFuelRates[i] * fuelPrices[i]));
                    total = total + ((summ * 100) / (vanFuelRates[i] * fuelPrices[i]));
                }
                break;
            case R.id.chooseTruck:
                chooseTruck.getBackground().setAlpha(100);
                chooseVan.setBackgroundResource(R.drawable.imageview_red_border);
                final double[] truckFuelRates = {32 /*CNG*/, 25 /*Diesel*/, 31 /*AI95*/, 31 /*AI92*/, 42 /*SUG*/};
                if (getChargeAmount.getText() == null) {
                    summ = Double.parseDouble(getChargeAmount.getText().toString());
                } else {
                    Toast.makeText(getActivity().getApplicationContext(), "The planned amount of fuel should be the number", Toast.LENGTH_LONG).show();
                }
                for (int i = 0; i <= 5; i++) {
                    double[] resArray = new double[5];
                    resArray[i] = ((summ * 100) / (truckFuelRates[i] * fuelPrices[i]));
                    total = total + ((summ * 100) / (truckFuelRates[i] * fuelPrices[i]));
                }
                break;
            default:
                Toast.makeText(getActivity().getApplicationContext(), "Choose car type", Toast.LENGTH_SHORT).show();
                break;
        }
    }
}

CalcFragment

public class CalcFragment extends Fragment {
    private Context mContext;
    private Activity mActivity;
    private CoordinatorLayout mCLayout;
    private Toolbar mToolbar;
    private TabLayout mTabLayout;
    private ViewPager mViewPager;
    private TabLayout tabLayout;
    private AppBarLayout mAppBarLayout;
    private CalcViewModel calcViewModel;

    public View onCreateView(@NonNull LayoutInflater inflater,
                             ViewGroup container, Bundle savedInstanceState) {
        calcViewModel =
                ViewModelProviders.of(this).get(CalcViewModel.class);
        View root = inflater.inflate(R.layout.fragment_calc, container, false);

        // Get the application context
        mContext = getActivity().getApplicationContext();
        mActivity = getActivity();

        // Get the widget reference from XML layout
        mCLayout = root.findViewById(R.id.coordinator_layout);
        mToolbar = getActivity().findViewById(R.id.toolbar);
        mTabLayout = root.findViewById(R.id.tab_layout);
        mViewPager = root.findViewById(R.id.view_pager);

        // Set a title for toolbar
         mToolbar.setTitle(getResources().getString(R.string.menu_calc));

        // Set the support action bar
        ((AppCompatActivity) getActivity()).setSupportActionBar(mToolbar);

//        ((AppCompatActivity)getActivity()).getSupportActionBar().setDisplayHomeAsUpEnabled(true);

        // Initialize a new instance of PagerAdapter
        PagerAdapter adapter = new SimpleFragmentPagerAdapter(
                getFragmentManager(),
                mActivity
        );

        // Set a PagerAdapter for ViewPager
        mViewPager.setAdapter(adapter);

        // Setup the TabLayout with ViewPager
        mTabLayout.setupWithViewPager(mViewPager);

        mAppBarLayout = getActivity().findViewById(R.id.mAppBarLayout);
        mAppBarLayout.setElevation(0);

        return root;
    }
}